A counterbored hole is usually used for when the top of a screw or bolt needs to be flush with, or sit just beneath, the surface of the material it is inserting.
An example of a shoulder screw and the corresponding counterbore hole is shown in this 3D model:
Use the image and chart below to determine what dimensions to use, all dimensions are in inches.
For example, an ANSI Inch 5/8″ shoulder screw with a normal fit counterbored hole will require a pilot hole diameter of 13/16″, a counterbore diameter of 1 1/8″, and a counterbore depth of 1/2″.
Counterbore Hole Size Chart for Shoulder Screw Fasteners (ANSI Inch)
All dimensions are in inches.
Fastener Size (Thread) | Pilot Hole Diameter (Close Fit) | Pilot Hole Diameter (Normal Fit) | Pilot Hole Diameter (Loose Fit) | Counterbore Diameter | Counterbore Depth |
| #10 | 17/64 | 9/32 | 19/64 | 7/16 | 16/85 |
| 1/4 | 21/64 | 11/32 | 23/64 | 1/2 | 16/73 |
| 5/16 | 25/64 | 13/32 | 27/64 | 5/8 | 1/4 |
| 3/8 | 17/32 | 9/16 | 39/64 | 13/16 | 5/16 |
| 1/2 | 21/32 | 11/16 | 47/64 | 1 | 3/8 |
| 5/8 | 25/32 | 13/16 | 29/32 | 1 1/8 | 1/2 |
| 3/4 | 1 3/32 | 1 1/32 | 1 5/32 | 1 1/2 | 5/8 |
| 7/8 | 1 9/32 | 1 31/90 | 1 7/16 | 1 7/8 | 3/4 |
| 1-1/8 | 1 9/16 | 1 5/8 | 1 47/64 | 2 1/4 | 1 |
| 1-1/4 | 1 13/16 | 1 7/8 | 2 | 2 1/2 | 1 1/8 |
| 1-1/2 | 2 1/16 | 2 1/8 | 2 1/4 | 2 7/8 | 1 1/4 |
If you want to learn more about counterbored holes, see our post here.