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 pan head 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 #1 pan head bolt with a normal fit counterbored hole will require a pilot hole diameter of 4/45″, a counterbore diameter of 11/64″, and a counterbore depth of 6/95″.
Counterbore Hole Size Chart for Pan Head Fasteners (ANSI Inch)
All dimensions are in inches.
Fastener Size | Pilot Hole Diameter (Close Fit) | Pilot Hole Diameter (Normal Fit) | Pilot Hole Diameter (Loose Fit) | Counterbore Diameter | Counterbore Depth |
| #0 | 1/15 | 6/79 | 3/32 | 9/64 | 2/37 |
| #1 | 3/37 | 4/45 | 8/77 | 11/64 | 6/95 |
| #2 | 3/32 | 7/69 | 7/62 | 3/16 | 7/97 |
| #3 | 5/47 | 8/69 | 9/70 | 7/32 | 3/37 |
| #4 | 3/25 | 9/70 | 14/97 | 1/4 | 8/89 |
| #5 | 9/64 | 5/32 | 11/64 | 9/32 | 8/77 |
| #6 | 2/13 | 10/59 | 5/27 | 19/64 | 7/62 |
| #8 | 9/50 | 10/51 | 13/61 | 23/64 | 10/77 |
| #10 | 15/73 | 21/95 | 5/21 | 13/32 | 4/27 |
| #12 | 15/64 | 15/61 | 6/23 | 29/64 | 1/6 |
| 1/4 | 17/64 | 9/32 | 19/64 | 17/32 | 8/39 |
Fastener Size | Pilot Hole Diameter (Close Fit) | Pilot Hole Diameter (Normal Fit) | Pilot Hole Diameter (Loose Fit) | Counterbore Diameter | Counterbore Depth |
| 5/16 | 21/64 | 11/32 | 23/64 | 41/64 | 24/97 |
| 3/8 | 25/64 | 13/32 | 27/64 | 25/32 | 16/55 |
| 7/16 | 29/64 | 15/32 | 31/64 | 57/64 | 1/3 |
| 1/2 | 17/32 | 9/16 | 39/64 | 1 1/64 | 31/82 |
| 9/16 | 19/32 | 5/8 | 43/64 | 1 5/64 | 8/19 |
| 5/8 | 21/32 | 11/16 | 47/64 | 1 13/64 | 45/97 |
| 3/4 | 25/32 | 13/16 | 29/32 | 1 15/32 | 27/49 |
If you want to learn more about counterbored holes, see our post here.