That is hole that has been drilled, then had a thread 'tapped' into it so you can insert a machine screw or bolt.
To help pull the bit into the surface being drilled and the spiral on the bit gives the material from the hole a place to go and pulls it out of the hole.
depends on where you put the hole and the load on the timber you're drilling thru. check with your local bldg. dept.
Yes and no. They leave the steel casing in the hole, and usually fill it with lean cement.
When a well is drilled and the drill is removed, all that is left is a hole in the earth/rock. If left that way, the hole could partially or completely collapse. To avoid this, a casing is inserted into the well hole. Usually this is a metal pipe, but it does not have to be made of metal. In the past, stones or bricks were laid by hand to fulfill this purpose. In some cases, a plastic pipe is sufficient.
A 3/16 inch pilot hole should be drilled for a 10 screw.
A pilot hole of 3/32 inch should be drilled for a 6 screw.
The size of the hole drilled for a door knob should typically be 2 1/8 inches in diameter.
A 3/16 inch pilot hole should be drilled for a 12 wood screw.
A 3/32 inch pilot hole should be drilled for a 10 wood screw.
A 7/64 inch pilot hole should be drilled for a 8 wood screw.
A 5/32 inch pilot hole should be drilled for a 3/8 lag screw.
A 3/16 inch pilot hole should be drilled for a 1/4 inch lag screw.
The relevance is some fool drilled a hole in it.
A 1/4 inch pilot hole should be drilled in wood for a 1/2 inch lag screw to ensure proper installation.
To accommodate a 3/8 bolt, drill a hole that is 3/8 inch in diameter.
A counterbored hole in engineering is used to create a recessed area at the top of a drilled hole. This allows for a screw or bolt head to sit flush with the surface. It is different from a regular drilled hole because it has a wider diameter at the top to accommodate the head of the fastener.