Diameter and thread count refer to the size of screw or bolt the threaded insert is used with. For example, a 1/4"-20 threaded insert fits a 1/4"-20 bolt.
10-32 is a fine thread, but it is listed under coarse thread because it is very common.
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Drill bits are cutting tools used to remove material to create holes.
A type of nut used to create internal machine threads in wood or similar materials.