Countersinking Guidelines
Precision countersinking for flush-mount fastener holes in your sheet metal parts. Countersinks are integrated into your production run — no separate processing step needed.
Design Requirements
Hole-to-Edge Distance
The distance from the hole center to the nearest edge must be at least the countersink outer diameter.
Hole-to-Bend Distance
Minimum distance from hole center to a bend line is 2 × thickness + bend radius. See the materials table for values per thickness.
Countersink Angles
82° — Imperial / SAE
ANSI/ASME B18.6.3 standard. For flat-head machine screws and general-purpose flush mounting.
90° — Metric / DIN
DIN 965 / ISO 10642 standard. For metric flat-head screws and European standard hardware.
82° Countersink Chart (Imperial)
ASME B18.6.3 flat-head screw dimensions.
| Bolt Size | Hole Diameter | Outer Diameter | Min Edge Distance |
|---|---|---|---|
| #4 | 3.28mm (0.129") | 6.48mm (0.255") | 6.48mm (0.255") |
| #6 | 3.81mm (0.150") | 7.80mm (0.307") | 7.80mm (0.307") |
| #8 | 4.50mm (0.177") | 9.12mm (0.359") | 9.12mm (0.359") |
| #10 | 5.11mm (0.201") | 10.44mm (0.411") | 10.44mm (0.411") |
| 1/4 | 6.76mm (0.266") | 13.49mm (0.531") | 13.49mm (0.531") |
| 5/16 | 8.08mm (0.318") | 16.66mm (0.656") | 16.66mm (0.656") |
| 3/8 | 10.32mm (0.406") | 19.35mm (0.762") | 19.35mm (0.762") |
| 1/2 | 14.29mm (0.563") | 22.23mm (0.875") | 22.23mm (0.875") |
90° Countersink Chart (Metric)
DIN 7991 / ISO 10642 flat-head screw dimensions.
| Bolt Size | Hole Diameter | Outer Diameter | Min Edge Distance |
|---|---|---|---|
| M2 | 2.41mm (0.095") | 4.39mm (0.173") | 4.39mm (0.173") |
| M2.5 | 2.90mm (0.114") | 5.50mm (0.217") | 5.50mm (0.217") |
| M3 | 3.40mm (0.134") | 6.73mm (0.265") | 6.73mm (0.265") |
| M4 | 4.50mm (0.177") | 8.97mm (0.353") | 8.97mm (0.353") |
| M5 | 5.51mm (0.217") | 11.20mm (0.441") | 11.20mm (0.441") |
| M6 | 6.60mm (0.260") | 13.44mm (0.529") | 13.44mm (0.529") |
| M8 | 9.00mm (0.354") | 18.25mm (0.719") | 18.25mm (0.719") |
| M10 | 11.00mm (0.433") | 22.73mm (0.895") | 22.73mm (0.895") |
| M12 | 13.50mm (0.531") | 27.21mm (1.071") | 27.21mm (1.071") |
Volume Pricing
Better per-countersink pricing with larger quantities:
| Quantity | Price per Countersink |
|---|---|
| 1+ | $0.75 |
| 10+ | $0.60 |
| 50+ | $0.50 |
| 100+ | $0.40 |
| 500+ | $0.30 |
Design Tips
CAD File Requirements
- Only include the minor (inner) hole diameter in your CAD file
- Countersinks detected from STEP files are matched automatically
- You can also configure countersinks manually in the quote tool
Best Practices
- Match countersink angle to fastener spec — 82° for ANSI, 90° for metric
- Verify outer diameter matches the fastener head for a flush fit
- Consider assembly accessibility when choosing top or bottom placement
- Adds 1 day to production lead time
Questions? Contact support@rmfg.com for help with countersink specifications or custom requirements.