Hand Tools

Sockets

The socket (Table 3-8) consists of a round metal sleeve with a square opening cut in one end

for insertion of a handle, and a 6 point or 12 point wrench opening in the other. They are

available in both common (short) and deep (long) lengths. The length of the socket does not

determine its size. The openings that fit onto the bolt or nut determines the size and is

graduated in 1/16-inch increments.

In using the 12 point socket, you need to turn it only half as far as the 6 point socket before

lifting it from the nut and refitting it to the nut for a new grip. It can therefore be used in

closer quarters where there is less room to move the handle. Determine a socket’s size

according to two factors: one is the size of the square opening, which fits on the square drive

lug of the handle. This size is the drive size. The other is the size of the opening in the

opposite end, which fits the nut or bolt. Composite Tool Kits can be outfitted with sockets

having, 1/4, 3/8, and 1/2 inch square drive lugs.

Socket Handles

There are many different types of handles (Table 3-8) used with sockets. Each type has

special advantages, and the experienced crew chief chooses the best one suited for the job at

hand. The square driving lug on a socket handle has a spring-loaded ball that fits into a recess

hole in the socket’s square driving receptacle. This mated ball and recess feature works to

prevent the socket from detaching off the handle.

Socket Handles

There are many different types of handles (Table 3-8) used with sockets. Each type has

special advantages, and the experienced crew chief chooses the best one suited for the job at

hand. The square driving lug on a socket handle has a spring-loaded ball that fits into a recess

hole in the socket’s square driving receptacle. This mated ball and recess feature works to

prevent the socket from detaching off the handle.

Table 3-8, Socket Handles

Sockets

A socket is a cylindrical tool with a different shaped

socket at each end. At one end there’s a prismatic hole

that fits over the head of a fastener. This hole is most

commonly hexagonal to fit the head of a hex-head bolt

or hexagonal nut. However, several types of sockets are

available to fit a variety of fasteners.

On the opposite end of the socket is a square hole that

engages with another tool to drive the socket. The

square drive is either 1/4, 3/8, 1/2 or 3/4-in. Metric

sockets still use these sizes for the drive.

Ratchets

The ratchet handle has a reversing lever that operates a

pawl inside the head of the tool. Pulling the handle in

one direction causes the pawl to engage the ratchet

teeth and turn the socket. Moving the handle in the

opposite direction causes the pawl to slide over the

teeth, permitting the handle to back up without moving

the socket. This allows rapid turning of the nut or bolt

after each partial turn of the handle. With the reversing

lever in one position, the handle tightens the bolt/nut.

In the other position, it loosens the bolt/nut. Use the

ratchet for speed and convenience in places where you

cannot make a full 360° turn because of obstructions

near the fasteners.

Hinged Handle

The hinged handle is also very convenient. The hinged

handle is the longest and strongest socket handle. It has

a hinged adapter at one end used to break torque on a

nut or bolt. After loosening the nut to the point where it

turns easily, remove the handle and then turn the handle

with your fingers, or change the handle to a ratchet

handle to finish removing the nut or bolt.

Sliding T-bar

Use the “Sliding T-bar” handle in a similar fashion as

the hinged handle to break torque. When you are using

the sliding T-bar, the head can be positioned anywhere

along the sliding bar. Select the position that is best for

the job at hand. This provides you with increased

leverage in limited access areas.

Speed Handle

Use the speed handle for speed and convenience where

you can make a full 360° turn of the handle. After

loosening the bolts/nuts with the hinged handle or

sliding T-bar, you can switch to the speed handle and

use it to remove the bolts and nuts with greater speed.

Attachments

Many mechanics think the ratchet is the heart

of the tool box. But the attachments play a very

important role for the maintenance of aircraft.

Different jobs need different attachments

(Table 3-9), (fig. 3-168) to remove and install

all types of fasteners.

Table 3-9, Attachments

Extensions

 Designed to allow access to fasteners in

recessed areas

 Made in various lengths and drive sizes

Universals

 Allows access to nuts or bolts from various

angles

 Available in multiple drive sizes

Adapters

 Makes changes to drive sizes on sockets,

extensions, and handles

 Used to increase or decrease drive size, thus

allowing different drive size sockets to be

used

Crow Foot

The crowfoot wrench (fig. 3-169) is an open-end

wrench head used with a socket handle for tightening

and loosening fittings on plumbing or in limited access

applications where an obstruction would prevent the

use of a regular socket.

Wrenches

A wrench is a tool specially designed to tighten or loosen nuts, bolts, studs, and pipes. There

are many different types of wrenches (Table 3-10). Each type has its own use. By using the

proper wrench correctly for the task to be done, you will not break the wrench, damage the

equipment, or cause personal injury. You use wrenches to exert a turning (twisting) force on

bolts, nuts, etc. There are a few basic rules that you should keep in mind when using

wrenches. They are as follows:

• Always use a wrench that fits the nut properly.

• Keep wrenches clean and free from oil. (May slip, resulting in serious injury)

• Do not increase the length of a wrench by placing a pipe over the handle. (Increased

leverage may damage the wrench or the hardware)

• Learn to select your wrenches to fit the type of work you are doing.

Table 3-10, Wrenches

Open-end Wrenches

All open-end wrenches have open jaws on one

or both ends of the wrench. The size of the

jaw opening normally determine the length of

the wrenches. These wrenches are sized the

same as box-end wrenches. The open smooth

faced ends of the wrench allow users to place

them on aircraft tubing and hose fittings. In

addition to the open design of the head, some

wrenches have an offset of 15°. This offset

works well in close quarter situations where

there is not enough clearance between the

fastener and an obstruction. A disadvantage of

these wrenches is the reduced number of

contact surfaces which means more chance of

it slipping from the fastener.

Box-end Wrenches

Box-end wrenches have a head on each end of

a bar. The head surrounds the nut or bolt head

on all sides, which decreases the chances that

the wrench will slip and provides the best

protection to you and the equipment. Box-end

wrenches are available with 6-point or

12-point openings. The 12-point opening is

more common, as it works on both square and

hexagonal bolt heads. Some wrenches have

the same 15° offset for the same purpose as

the open-end wrench. The major disadvantage

of the box-end wrench is that there must be

enough clearance above and around the bolt

head to place the wrench over it.

Adjustable Jaw Wrench

The adjustable jaw wrench has one fixed

jaw and a movable or adjustable jaw. The

adjustable jaw is set against the face of the

nut by turning a knurled worm gear. Use an

adjustable jaw wrench for the removal

and/or installation of nuts/bolts when the

correct size open-/boxed-end wrench or

socket is not available. The overall length

in inches or millimeters determines the

wrenches size. When using the adjustable

jaw wrench place the pressure against the

stronger stationary jaw to prevent damage

to the hardware, the wrench, or injury to

you.

Hex Wrench

The hex wrench is an L-shaped, six-sided

wrench. Both ends of the “L” are the same

size so you can turn the wrench either to

gain access to the screw head or to obtain

an advantage with leverage. Use the hex

wrench to remove and/or install hex head

(internal wrenching) bolts and set screws.

Hex wrench sizes are determined by

measuring across the face of the wrench

from two opposing flat surfaces.

Screwdrivers

Screwdrivers are available in many different shapes and sizes (Table 3-11). Use screwdrivers

for driving or removing screws with slotted, recessed, or special heads. The proper way to

select and use a screwdriver is to match the screwdriver to the type/size of screw head. The

two most commonly classified screwdrivers are the flat tip (common) and the cross tip. They

all follow the basic design of a handle, attached to a shank with a style of blade at the end

(fig. 3-170). The style of the blade determines the type of screwdriver. The overall length of

the shaft and blade, excluding the handle, determines the length of a screwdriver.

Screwdrivers, like any other hand tool, are dangerous when not used properly. Therefore, you

should always follow these safety precautions:

• The tip of the screwdriver (fig.3-171) must fit the slot of the screw head snugly.

• You must use screwdrivers for their intended purpose. For example; Reed and Prince

Screwdrivers and Phillips screwdrivers are not interchangeable. Always use a Reed and

Prince Screwdriver with Reed and Prince Screws, and a Phillips screwdriver with Phillips

screws. The use of the wrong screwdriver will result in mutilation of the screw head.

• Do not use a screwdriver for prying, punching, chiseling, scoring, or scraping.

• Never use a screwdriver to check an electrical circuit.

• Never try to turn a screwdriver with a pair of pliers.

• NEVER GET ANY PART OF YOUR BODY IN FRONT OF THE SCREWDRIVER

BLADE TIP. (This is a good safety rule for any sharp or pointed tool.)

Flat-Tip (common)

Use the standard, flat-tip, or common screwdriver on fasteners

having a common slotted head.

Phillips

Use the Phillips screwdriver on fasteners with cross-slots

having rounded corners and a blunt tip.

Prince and Reed

Use the Prince and Reed screwdrivers on fasteners with crossslots

having square corners and a sharp tip.

Hi Torque Tip (coin slot)

This is a variation of the flat tip type screwdriver with round

edges like the edges of coins. Its design allows the blade to

reach deeper into the fastener for applying higher removal and

installation torque.

Offset Screwdriver

Offset screwdrivers utilize a 90° bend at both ends of the blade

to allow access to places where space is limited. They may

have either a flat-tip or a cross-tip.

Torque-Set

This torque-set screwdriver is like the cross-tips; however, the

edges of the tips offset. It allows for higher installation and

removal torque.

Hex

Hex end screwdrivers present an alternative to using hex

wrenches for internal wrenching screws and set screws.

Apex-Bit Holder

Use an Apex-bit holder to hold securely Apex-bits

(screwdriver type tips). Use them with socket handles to

provide screwdriver like characteristics.

Hammers

As simple as the hammer is, there is a right and a wrong way to use it (fig. 3-172). They all

share the same basic design. The size, shape, and material determine a hammers’ purpose.

The two, shown in Table 3-12, below represent those most commonly used in aircraft

maintenance.

Hammers are dangerous tools when used carelessly and without consideration. You will use

hammers for driving chisels and punches, shaping metal, and installing components by

striking the surface. Use of proper eye protection is important and required when using

hammers.

Table 3-12, Hammers

Ball Peen

You determine the size of a ball peen hammer by the

weight of the head in ounces. Its hardened steel head has

a flat face with a round (peen) portion on the opposite

end. All ball peen hammers have a flat striking face on

one end of the head for striking punches and chisels.

Use the other end, the peen end for forming, expanding

and shaping soft metal, and peening rivet heads.

Mallet

Mallets provide a means of striking soft metal for forming

and shaping, highly polished surfaces without damaging

the surface and in situations where a hammer may

produce a spark. The head is made of wood, rubber,

rawhide leather, plastic, or brass.

Pliers

Many different types of pliers are in use today (Table 3-13). Pliers offer crew chiefs the

ability to perform several tasks that involving gripping surfaces, reaching into tight areas,

holding components in place, and cutting materials. Their basic design combines two handles

held together with a pivot pin. The end of the tool determines its intended use.

Table 3-13, Pliers

Common Slip Joint

The slip-joint pliers have adjustable jaws that can

change between two jaw-opening widths using a slip

joint. Use the pivot to adjust the jaw opening to handle

large or small objects. The tips of the jaws provide a

means to grip objects with fine teeth near the end and

coarse teeth near the throat.

Multiple Slip Joint

These pliers are like the common slip-joint pliers.

Instead of the single joint, they have several slip-joints

to provide multiple jaw widths. The variable size of the

jaws provides gripping capabilities for a tighter or

wider grip as needed.

Locking Pliers

Locking pliers have a locking feature that permits you

to lock the pliers onto an object. You can adjust them

to various jaw openings by turning the knurled

adjusting screw at the end of the handle. By pulling the

lever toward the handle, locking pliers clamp and lock

in position. In addition, you may use them as a clamp,

portable vise, and for many other uses where a locking,

plier-type jaw may be used. However, you should use

locking pliers with care since the teeth in the jaws tend

to damage the object on which they clamp. You should

not use them on nuts, bolts, tube fittings, or other

objects if you plan to reuse the item

Long Nose

Use long nose pliers to reach into places too small for

fingers. Long nose jaws taper to a point, have

serrations at the nose end and a side cutter near the

throat. Use long nose pliers to hold small items steady,

to cut and bend wire, or to do numerous other jobs that

are too intricate or too difficult to be done by hand

alone.

Duck Bill

Duckbill pliers have long wide jaws and slender handles.

Use duckbills in confined areas where you cannot use

your fingers. The scored jaw faces of the pliers aid in

holding an item securely. In addition, they work well for

pulling and twisting safety wire.

Diagonal Side Cutters

Diagonal side-cutters are an important tool for you to

use. Use them for cutting small wire, cotter pins, and

other small diameter metal items. The inner jaw surface

is a diagonal straight cutting edge offset approximately

15-degrees. This design permits cutting objects flush

with the surface. The design of the diagonal side-cutter

pliers does not allow for the holding of objects. If used

to hold an object, the pliers will cut or deform the

material.

Safety Wire Pliers

When installing equipment, you may need to lock wire

(usually referred to as safety wire) designated parts of

the installation. You can accomplish the process of

safety wiring faster and neater with the use of safety

wire pliers. Safety wire pliers are three-way pliers—they

hold, twist, and cut. Designed to make a uniform twist

and to reduce the time required in twisting double-strand

safety wire.

Safety Wire Pliers Operation (fig. 3-173)

To operate, grasp the wire between the two diagonal jaws of the pliers. As you squeeze the

handles together, use your thumb and forefinger to bring the inner (locking) sleeve into the

locked position. Make sure the wire does not become kinked or nicked during twisting

operation. If wire is damaged, replace with new wire. A pull on the knob of the pliers makes a

uniform twist. Push the spiral rod back into the pliers without unlocking them, and by again

pulling on the knob, you can make a tighter twist. Install the wire snugly but not so tight that

the wire is overstressed (Table 3-14). A squeeze on the handles unlocks the pliers, and then

you can use the safety wire pliers to cut the wire to the proper length using the cutting jaws.

These actions all work to speed up the double twist method of safety wiring.

Table 3-14, Safety Wire Twists

Safety Wire Size Number of Twists (per inch)

.020 gauge wire 9-12 turns

.032 gauge wire 7-12 turns

.041 gauge wire 7-10 turns

Safety Wire pliers are used for the double twist method (fig. 3-174). When securing widely

spaced bolts by the double twist method, the maximum number of bolts that can be wired in a

series is 3. Screws or bolts in closely spaced geometrical pattern will use the single wire

method (fig. 3-175). When securing closely spaced bolts, the number that can be secured by a

24-inch length of wire is the maximum number in a series.

Miscellaneous Tools

Composite Tool Kit (CTK) do not always have all the tools necessary to do a job. Sometimes

you will require the use of miscellaneous tools. Listed in the next few paragraphs are a few of

the miscellaneous tools you may use.

Center Punch

The center punch (fig. 3-176), as the name implies, is used for marking the center of a hole to

be drilled by striking it with a hammer. If you try to drill a hole without first punching the

center, the drill will “wander” or “walk away” from the desired center. A center punch also

secures pins inside hinges by denting the end of the hinge hole.

Chisel

The type of chisel most commonly used is the flat cold chisel (fig. 3-176). The cold chisel

uses a sharp, beveled edge to cut rivets, split nuts, chip castings, and cut thin metal sheets.

When using a chisel, always wear goggles (eye protection) to protect your eyes.

Cotter Pin Extractor

The cotter pin extractor is a steel bar with a curved taper on one end and a curved wedge on

the other. Use this S-shaped tool (fig. 3-176) to install or to remove cotter pins. Insert the

point of the taper into the eye of the cotter pin to remove it. Use the curved wedge end to bend

or straighten the ends of a cotter pin.

Mechanical Fingers

With the mechanical fingers, you can retrieve small articles (objects) that have fallen into

places where you cannot reach them by hand. You can also use this tool when starting nuts or

bolts in difficult areas. The mechanical fingers (fig. 3-177) have a tube containing flat springs

that extend from the end of the tube to form claw like fingers when thumb pressure is applied

to the flat end of the rod. When the user releases the thumb pressure, the tool’s fingers retract

back into the tube as far as the object retrieved will allow. Thus, the fingers apply enough

pressure on the object to hold it securely. Some mechanical fingers have a flexible end on the

tube to permit their use in close quarters or around obstructions.

measures very small gaps between fitted parts.

Inspection Mirror

Several types of inspection mirrors are available for use in maintenance. Mirrors come in a

variety of sizes and may be round or rectangular. The mirror connects to the end of a rod, and

it may be fixed or adjustable. The inspection mirror (fig. 3-178) aids you in making detailed

inspections where you cannot directly see the inspection area.

Measuring Tools

When performing some maintenance tasks, you must take measurements to determine the

amount of service life remaining on a particular item, or to make sure replacement parts used

meet established specifications. The accuracy of these measurements often affects the

performance and failure rates of the concerned equipment. Some of the measurement tools are

very sensitive and require calibration periodically by the Precision Measurement Equipment

Laboratory (PMEL).

Thickness Gauge

Use a thickness gauge

(fig. 3-179) for precision

measurement of very close

gaps between fitted parts.

When you use a combination

of blades to get a desired

thickness, place the thinner

blades between the heavier

ones to protect the thinner

blades and to prevent their kinking. Do not force blades into openings that are too small; the

blades may bend and kink. Most thickness gauges have different graduated sized blades. The

graduated sized blades measure in thousandths of an

inch or millimeters.

Ruler

Of all measuring tools, the simplest and most common

is the ruler (fig. 3-180). The ruler is usually 6 or 12

inches long, although other lengths are available. The

longest lines represent the inch marks. Using the ruler

in figure 3-180, you see that on one edge, each inch

divides into 8 equal spaces, so each space represents 1/8

inch. The other edge of this ruler divides into

sixteenths.

Torque Wrench

A force that produces a rotating or twisting motion is called

“torque”. For the nut to properly load the bolt and prevent

premature failure, you must apply a designated amount of

torque to the nut. Proper torque, with a torque wrench

(fig. 3-181), reduces the possibility of fasteners loosening

while your aircraft is in flight.

The three most commonly used torque wrenches are the

deflecting beam, dial indicating, and micrometer setting types

(breakaway). The torque amounts measure in inch-pounds

(in-lbs.) or foot-pounds (ft-lbs.). When using the deflecting

beam and the dial indicating torque wrenches, read the torque

on the dial or scale mounted on the handle of the wrench.

Torque Range

Based on the amount of torque called for in your technical

order you make the proper torque wrench selection for the task. You will select a proper size

torque wrench for the job in both areas of torque range and drive size. Do not use the tool if it

is within the lower 20% of its operating range.

Setting the torque value (fig. 3-182) requires you to read a combined setting from a vertical

and horizontal scale. The vertical scale contains torque settings from lowest to highest,

graduated in large-scale increments. The horizontal scale makes small adjustments in the

torque settings between each of the larger increments of the vertical scale.

Reading the torque handle setting is not difficult. In the given example of a breakaway torque

wrench (fig. 3-182), each mark on the vertical scale represents 10 foot-pounds of torque and

the horizontal scale (on the top of the handle) represents 1 foot-pound values. Rotating the

handle until a desired set of numbers line up on each scale sets the torque value. As shown on

the left, the vertical scale indicates 50 foot-pounds and 54 foot-pounds in the right picture. To

use the micrometer setting type of torque wrench, unlock the grip and adjust the handle to the

desired setting on the micrometer-type scale, then relock the grip. Install the required socket

or adapter to the square drive of the handle. Place the wrench assembly on the nut or bolt and

pull in a clockwise direction with a smooth, steady pulling motion. (A fast or jerky motion

will result in an improperly torqued bolt or nut). When the torque applied reaches the torque

value, a signal mechanism will automatically give an audible click, and the handle will

release/break over, and move freely for a short distance. You can easily feel the release and

the free travel if you do not use a fast, jerky motion, so there is no doubt about when the

torquing process is complete

Precautions for Use

Torque wrenches are delicate and expensive tools. YOU MUST ENSURE TORQUE

WRENCH CALIBRATIONS ARE NOT OVERDUE. The precision nature of torque

wrenches requires many precautions to ensure it performs correctly. Technicians must check

the calibration information located on the decal for the wrench; overdue dates make the

wrench unserviceable for use. Torque wrenches measure the force applied to a fastener;

therefore, NEVER use a torque wrench to loosen hardware items. Additionally, if you drop

the wrench or it strikes against a hard surface, return it to the support section for calibration.

You must properly apply torque using a smooth, pulling motion and stop immediately when

the wrench gives you indication that you applied the desired torque value. Once the task is

completed, you will set the torque wrench to its lowest value indicated on the vertical scale.

Do not move the setting handle below the lowest torque setting because it damages the

wrench internally and makes it unserviceable.

Prevailing (Running) Torque

Prevailing torque is a procedure for checking the serviceability of locking hardware such as

self-locking screws and nuts for the possible re-use on the aircraft or component. To obtain

the correct recommended torque value on a nut, the nut must be run down until it is one turn

from the beginning of seating. Once reached, note the prevailing torque. If the prevailing

torque is less than one-third of the recommended torque, it should be disregarded, and the nut

tightened to the recommended torque value. If the prevailing torque is one-third or more than

one-third of the recommended torque, it should be added to the recommended torque. It is not

always necessary to account for prevailing torque. If the appropriate TO specifies using a selflocking

screw or nut and does not state that prevailing torque should be compensated for, it

must be assumed that the manufacturer of the item has already taken it into consideration.

Prevailing torque will be compensated for only if required by specific technical data.

Example: The recommended torque is 50 to 70 inch-pounds, and it takes 30 in-lbs. of torque

just to make the nut turn because it is a lock nut. Then the correct torque wrench setting would

be 80 to 100 inch-pounds (30 inch-pounds higher to account for prevailing torque). If the

prevailing torque had been 10 inch-pounds, it would have been disregarded and the correct

torque wrench setting would have been 50 to 70 inch-pounds.

Tension meter

The Tension meter (fig. 3-183) is an instrument used in

checking cable tension and cable size (diameter). Tension

is the amount of pulling force applied to the cable. The

Tension meter, like any other measuring instrument, is a

delicate piece of equipment and it requires calibration.

Tension meters should never be stored in a toolbox. In

addition, it is critical to remember that while rigging flight

controls, temperature changes affect the cable’s tension.

For safe and efficient operation, the Air Force uses fluid

power (gasses, liquids) systems designed to operate at a

specific pressure, or within a pressure range. Most fluid

power systems come provided with pressure gauges for

measuring and indicating the pressure in the system.

Maintainers refer to many pressure-measuring instruments as

gauges. The pointer position indicates pressure. Most

measurements of pressure are in pounds per square inch

(psi). You must also check the pressure gauge for calibration

on the PMEL sticker.

Micrometer

Measurement tool for small distances or thicknesses usually graduated in thousandths of

inches that can be measured between two points of an object or assembly. The micrometer

(fig. 3-185) has one a movable face that can be moved towards or away from the fixed face by

turning a fine threaded adjustment screw and reading the scale near the adjustment screw.

Scales (fig. 3-186)

 The primary scale is located on the sleeve. This scale contains the 1mm

increment and half mm increment reading.

 The second scale is located on the thimble and has 50 marks.

How to Use the Scales (fig. 3-187)

 When you are measuring your object only count the exposed marks up to the

edge of the thimble. In the image you read 7mm. To measure into the

hundredth mm increments, use the index line to meet the mark on the Second

Scale on the thimble.

 From the example in the image, the measurement on the thimble is 0.14mm.

For the total reading simply add the measurement from the primary scale and

the measurement from the secondary scale. 7mm + 0.14mm = 7.14 mm.

Therefore, the measurement in the image is 7.14 mm.

Tip: If the half mm increment is showing on the primary scale, add 0.5mm to the total

reading.

Depth Gauge (fig. 3-188)

A precision instrument for measuring the depth of holes, slots, steps or other grooves or

concavities during maintenance. Tires will be the most common item this tool is used on to

measure the depth of usable tread or the depth of a cut in the tire comparable to the tread.