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Thread prep
Drill and Tap Size Chart
Select common tap drill starting points before calculating drilling RPM, tapping feed, and tapped-hole cycle time.
Direct answer: tap drill size depends on thread size, pitch, and target thread percentage before tapping feed is calculated. Verify thread class, material, plating, and tap style before release.
Thread prep
Drill and Tap Size Chart
Common inch and metric tap drill starting points for planning tapped holes before final thread percentage and material review.
Source: Created from the 2026-06-24 GSC shop-floor reference expansion; verify thread class, material, plating, and customer requirements before release.Updated: 2026-06-24
| Thread | Common tap drill | Approx thread percent | Planning note |
|---|---|---|---|
| #10-24 UNC | #25 / 0.1495 in | 70% - 75% | Check torque and material before increasing thread percent. |
| 1/4-20 UNC | #7 / 0.201 in | 70% - 75% | Common starting point for general shop use. |
| 5/16-18 UNC | F / 0.257 in | 70% - 75% | Use rigid tapping feed based on pitch after drilling. |
| 3/8-16 UNC | 5/16 / 0.3125 in | 70% - 75% | Confirm depth, chamfer, and chip evacuation. |
| M6 x 1.0 | 5.0 mm | About 75% | Adjust for forming taps or tough stainless materials. |
| M8 x 1.25 | 6.8 mm | About 75% | Verify thread callout before using metric coarse defaults. |
| M10 x 1.5 | 8.5 mm | About 75% | Use tapping calculator for RPM and pitch-based feed. |
Tapping feed
Calculate pitch-based feed after the drill size and thread pitch are confirmed.
Drilling setup
Set RPM and feed for the drilled hole before tapping or thread forming.
Cycle-time handoff
Estimate pecking, retracts, drill time, and setup allocation for holemaking.
Download chart
Use the PDF during programming and setup review.