A screw is a sharp piece of threaded metal similar to a nail. Unlike a nail, a screw has spiral grooves down its spike. A screw is pressed down against wood and turned with a screwdriver. Turning the screw to the right makes it go into the wood. The grooves cut into the wood. This prevents the screw from falling out, as a nail might. Turning the screw to the left pulls it out of the wood.
Screw threads are measured either in millimeters or in numbers. They are used in furniture, doors, appliances, etc.
Screwing and screwsEdit
Screwing is the neatest way of holding together two materials. If no glue is involved, then the screwing can be dismantled.
These are three different types of screw.
- Countersunk: First you drill a pilot hole into the wood. Then you can widen out the top by using a countersink drill bit. The head is flat on the top.
- Raised head: Has a slightly domed head, raised above the surface.
- Round head: Domed head above surface, broader than underneath.
Do not place screws in line as this weakens the wood. Use the right size screwdriver for the screw head. A screwdriver that is too slim can damage the slot, too wide can tear the materials. Screw threads in both wood and metal can become stripped, resulting in loss of holding power, and can also be difficult to remove.
A screw is a type of simple machine.