Unsure on what size countersunk hole to use for your ANSI Inch socket flat head fasteners?
Use the image and chart below to determine what dimensions to use, all dimensions are in inches apart from the countersink angle.
For example, an ANSI Inch 1/2″ flat head screw with a normal fit countersunk hole will require a pilot hole diameter of 9/16″, a countersunk diameter of 1″, and a countersunk angle of 82°.
Countersunk Hole Size Chart for Socket Flat Head Fasteners (ANSI Inch)
All dimensions are in inches apart from the countersink angle.
| Fastener Size (Thread) | Pilot Hole Diameter (Close Fit) | Pilot Hole Diameter (Normal Fit) | Pilot Hole Diameter (Loose Fit) | Countersink Diameter | Countersink Angle |
| #0 | 1/15 | 6/79 | 3/32 | 5/32 | 82 |
| #1 | 3/37 | 4/45 | 8/77 | 3/16 | 82 |
| #2 | 3/32 | 7/69 | 7/62 | 7/32 | 82 |
| #3 | 5/47 | 8/69 | 9/70 | 1/4 | 82 |
| #4 | 3/25 | 9/70 | 14/97 | 9/32 | 82 |
| #5 | 9/64 | 5/32 | 11/64 | 5/16 | 82 |
| #6 | 2/13 | 10/59 | 5/27 | 11/32 | 82 |
| #8 | 9/50 | 10/51 | 13/61 | 3/8 | 82 |
| #10 | 15/73 | 21/95 | 5/21 | 7/16 | 82 |
| 1/4 | 17/64 | 9/32 | 19/64 | 9/16 | 82 |
| Fastener Size (Thread) | Pilot Hole Diameter (Close Fit) | Pilot Hole Diameter (Normal Fit) | Pilot Hole Diameter (Loose Fit) | Countersink Diameter | Countersink Angle |
| 5/16 | 21/64 | 11/32 | 23/64 | 11/16 | 82 |
| 3/8 | 25/64 | 13/32 | 27/64 | 27/32 | 82 |
| 7/16 | 29/64 | 15/32 | 31/64 | 29/32 | 82 |
| 1/2 | 17/32 | 9/16 | 39/64 | 1 | 82 |
| 5/8 | 21/32 | 11/16 | 47/64 | 1 1/4 | 82 |
| 3/4 | 25/32 | 13/16 | 29/32 | 1 1/2 | 82 |
| 7/8 | 29/32 | 15/16 | 1 1/32 | 1 3/4 | 82 |
| 1 | 1 1/32 | 1 3/32 | 1 5/32 | 2 | 82 |
| 1 1/8 | 1 5/32 | 1 7/32 | 1 5/16 | 2 1/4 | 82 |
| 1 1/4 | 1 9/32 | 1 31/90 | 1 7/16 | 2 1/2 | 82 |
| 1 3/8 | 1 7/16 | 1 1/2 | 1 39/64 | 2 3/4 | 82 |
| 1 1/2 | 1 9/16 | 1 5/8 | 1 47/64 | 3 | 82 |