1.4 Wood Screws, Nuts and Bolts and Coach Bolts

Describe role of the shank as part of a wood screw

Often, part of the screw - known as the shank - does not have a thread. This makes it easier for screwing two pieces of timber together where the thread is only needed at the bottom.

How do you join two pieces of wood together with wood screws?

• When joining two pieces of wood together, the top part is drilled with a clearance hole that the screw simply pushes through.

• The bottom piece of timber has a pilot hole (thinner than the thread) so that the coarse pitch of the thread bites into the timber.

• Wood screws can have a countersink (conical head). This allows the screw to fit flush with the surface of the wood providing that a countersunk hole is drilled.

Name the three different forms of woods screws

• Slot head

• Phillips

• Pozidriv

Describe the suitablitiy of slot-head screws

Slot head screws are the simplest and most economical screw. They are tightened using a slot head screwdriver, but they are not really suitable for use with a power screwdriver. Slot head screws are often supplied with products to be fitted to a wall, such as mirrors or light fittings.

Describe the suitablitiy and proterties of Phillips screws

The Phillips screw was developed to improve contact with the screwdriver and increase the torque that can be applied. The design of the screw is such that it accepts the tip of a screwdriver with an angle of 57 degrees. If too much torque is applied, the screwdriver will slip. This avoids stripping the thread on the screw.

Describe the suitablitiy and proterties of Pozidriv screws

Pozidriv screws are a further refinement of the Phillips screw. They improve contact with the screwdriver and allow greater torque. Pozidriv screws are particularly good for using with power screwdrivers. Pozidriv screws are the preferred type of screw for woodworking jobs where multiple joints need to be fastened.

The addition of further diagonal slots on the screw make a better contact with the driver bit.

Decribe the appilcations and proterties of bolts including on how they are fixed

Bolts that are used to join wood pieces together - called 'coach bolts - have a thread that runs about two-thirds of the way along the bolt. Under the domed head of the bolt is a square piece that digs into the wood when tightened, preventing the bolt from rotating. This means that when the bolt is tightened, the domed head cannot be undone with a spanner. This is useful in fitting bolts or locks to wooden doors because it makes them secure if the domed part is on the outside.