Holes. Definitions and callouts. www6.district125.k12.il.us. counterbore. A counterbore can refer to a cylindrical flat-bottomed hole, which enlarges another hole. A spot face is a very shallow counterbore . .
Definitions and callouts
This the callout for a counterbore hole. It gives the diameter of the top and bottom holes and tells how deep both of them are (the top, larger hole is .266 deep, the bottom, smaller hole goes all the way through)
This is the callout for a countersunk hole that goes all the way through with a 2.06 diameter and has a top diameter of 3.71 that angles down at a 100 degree angle
The callout for this tapped hole tells that there are 4 identical holes (4X) the type of thread (3/4-10 UNC), and how deep it is
The clearance can be close, loose or normal
Here is a blind hole that is only .750 deep