This machine hex nut #4 mates with our #4-40 screw. The OD (outside diameter or outside clearance) is 0.112". The UNC (Unified National Coarse) is 40, the same as the #4 screw. Your hole size must be a minimum of 0.112" for the nut to fit. The ID (internal diameter) is 0.0925" (approximate). To tighten the nut you are going to need a socket size of 1/4".