Technically, a bolt is a machine. (Wire rope is a machine too.) The tighter your tolerances the more deeply you need to go into the details. For example, a hol

Technically, a bolt is a machine. (Wire rope is a machine too.) The tighter your tolerances the more deeply you need to go into the details. For example, a hole drilled by a two-flute drill isn't round nor straight and to make it so you need to broach or bore it. You need to check how much out-of round it is and you do that with a three-point ID micrometer, since a two-flute drill makes a roughly triangular hole. Then for straighness you need a set of pin gauges... The softer the material the less tolerances matter. This is why plastic is cheap and machine tools are expensive.