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 socket 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 2″ socket cap head bolt with a normal fit counterbored hole will require a pilot hole diameter of 2 1/8″, a counterbore diameter of 3 1/8″, and a counterbore depth of 2 1/16″.
Counterbore Hole Size Chart for Socket Cap 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 | 1/8 | 6/79 |
| #1 | 3/37 | 4/45 | 8/77 | 5/32 | 2/23 |
| #2 | 3/32 | 7/69 | 7/62 | 3/16 | 5/49 |
| #3 | 5/47 | 8/69 | 9/70 | 7/32 | 10/87 |
| #4 | 3/25 | 9/70 | 14/97 | 7/32 | 11/86 |
| #5 | 9/64 | 5/32 | 11/64 | 1/4 | 11/78 |
| #6 | 2/13 | 10/59 | 5/27 | 9/32 | 2/13 |
| #8 | 9/50 | 10/51 | 13/61 | 5/16 | 9/50 |
| #10 | 15/73 | 21/95 | 5/21 | 3/8 | 8/39 |
| 1/4 | 17/64 | 9/32 | 19/64 | 7/16 | 25/89 |
| 5/16 | 21/64 | 11/32 | 23/64 | 17/32 | 12/35 |
Fastener Size | Pilot Hole Diameter (Close Fit) | Pilot Hole Diameter (Normal Fit) | Pilot Hole Diameter (Loose Fit) | Counterbore Diameter | Counterbore Depth |
| 3/8 | 25/64 | 13/32 | 27/64 | 5/8 | 28/69 |
| 7/16 | 29/64 | 15/32 | 31/64 | 23/32 | 38/81 |
| 1/2 | 17/32 | 9/16 | 39/64 | 13/16 | 43/81 |
| 5/8 | 21/32 | 11/16 | 47/64 | 1 | 61/93 |
| 3/4 | 25/32 | 13/16 | 29/32 | 1 3/16 | 57/73 |
| 7/8 | 29/32 | 15/16 | 1 1/32 | 1 3/8 | 77/85 |
| 1 | 1 1/32 | 1 3/32 | 1 5/32 | 1 5/8 | 1 1/16 |
| 1 1/4 | 1 9/32 | 1 31/90 | 1 7/16 | 2 | 1 5/16 |
| 1 1/2 | 1 9/16 | 1 5/8 | 1 47/64 | 2 3/8 | 1 9/16 |
| 1 3/4 | 1 13/16 | 1 7/8 | 2 | 2 3/4 | 1 13/16 |
| 2 | 2 1/16 | 2 1/8 | 2 1/4 | 3 1/8 | 2 1/16 |
If you want to learn more about counterbored holes, see our post here.
Looking for a Different Standard of Counterbore Hole?
Counterbore Hole Size Chart for Socket Cap Head Fasteners (ISO 4762)
Counterbore Hole Size Chart for Socket Cap Head Fasteners (DIN 912)
Counterbore Hole Size Chart for Socket Cap Head Fasteners (JIS)
Counterbore Hole Size Chart for Socket Cap Head Fasteners (GB)
Counterbore Hole Size Chart for Socket Cap Head Fasteners (ANSI Metric)
Counterbore Hole Size Chart for Low Socket Cap Head Fasteners (DIN 7984)