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A screw is a sharp piece of threaded metal similar to a nail. Unlike a nail, a screw has spiraling grooves down its spike. A screw is pressed down against wood and spun with a screwdriver so the wood goes into the grooves. This prevents the screw from falling out, as a nail could. Screws are basically divided into wood screws, machine screws and self-tapping screws.
Screw threads are measured either in millimeters or in numbers. screws are used in furniture, doors, appliances, mechanical applications etc.
Screwing and screws
Screwing is the neatest way of holding together to materials. If no glue is involved, then the screwing can be dismantled. Screwing can be used to connect all materials.
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.