Precision machining reference for screw sizing and thread engagement. Pick a screw — get the tap drill, clearance hole, and quick link to the right parts.
3/8-16 Tap Drill Size and Clearance Hole
- Tap Drill: Soft Matl.
- 5/160.3125"
- 75% Thread Engagement
- Tap Drill: Hard Matl.
- Q0.3320"
- 50% Thread Engagement
- Clearance: Close Fit
- W0.3860"
- Clearance: Free Fit
- X0.3970"
Related sizes
About the 3/8-16 thread
3/8-16 is a UNC (Unified National Coarse) thread with a 0.3750" major diameter and 16 threads per inch, giving a minor diameter of 0.2983". In aluminum, brass and plastics, drill 5/16 (0.3125") for about 75% thread engagement. In steel, stainless and cast iron, step up to Q (0.3320") for about 50% engagement, which cuts tapping torque and the risk of a broken tap while keeping most of the thread's strip strength. For a 3/8" screw to pass through, drill W (0.3860") for a close fit or X (0.3970") for a free fit.
3/8-16 tap drill options by thread percentage
| Drill | Decimal | Thread | Use |
|---|---|---|---|
| 5/16 | 0.3125" | 77% | Soft matl. |
| O | 0.3160" | 73% | |
| P | 0.3230" | 64% | |
| 21/64 | 0.3281" | 58% | |
| Q | 0.3320" | 53% | Hard matl. |
Form (roll) tap: drill S (0.3480") for about 64% thread. Form taps displace metal instead of cutting it, so they need a larger hole than a cut tap, aimed here at 65% thread.
Cut-tap thread percentage = 76.98 × TPI × (major − drill), in inches. Smaller drills leave more thread but raise tapping torque; above about 75% the extra strength is small. Form tap drill = major − 0.0068 × thread % × pitch.
Tap drill & clearance hole chart
Printable tap drill chart (PDF)Every inch and metric size, ready to print, plus drill decimal equivalentsBrowse all 99 sizes
- #0-80
- #1-64
- #1-72
- #2-56
- #2-64
- #3-48
- #3-56
- #4-40
- #4-48
- #5-40
- #5-44
- #6-32
- #6-40
- #8-32
- #8-36
- #10-24
- #10-32
- #12-24
- #12-28
- #12-32
- 1/4-20
- 1/4-28
- 1/4-32
- 5/16-18
- 5/16-24
- 5/16-32
- 3/8-16
- 3/8-24
- 3/8-32
- 7/16-14
- 7/16-20
- 7/16-28
- 1/2-13
- 1/2-20
- 1/2-28
- 9/16-12
- 9/16-18
- 9/16-24
- 5/8-11
- 5/8-18
- 5/8-24
- 11/16-24
- 3/4-10
- 3/4-16
- 3/4-20
- 13/16-20
- 7/8-9
- 7/8-14
- 7/8-20
- 15/16-20
- 1"-8
- 1"-12
- 1"-20
- M1.5 x 0.35
- M1.6 x 0.35
- M1.8 x 0.35
- M2 x 0.4
- M2 x 0.45
- M2.2 x 0.45
- M2.5 x 0.45
- M3 x 0.5
- M3 x 0.6
- M3.5 x 0.6
- M4 x 0.7
- M4 x 0.75
- M4.5 x 0.75
- M5 x 0.8
- M5 x 1.0
- M5 x 0.9
- M5.5 x 0.9
- M6 x 1.0
- M6 x 0.75
- M7 x 1.0
- M7 x 0.75
- M8 x 1.25
- M8 x 1.0
- M9 x 1.25
- M9 x 1.0
- M10 x 1.5
- M10 x 1.25
- M10 x 1.0
- M11 x 1.5
- M12 x 1.75
- M12 x 1.5
- M12 x 1.25
- M14 x 2.0
- M14 x 1.5
- M14 x 1.25
- M15 x 1.5
- M16 x 2.0
- M16 x 1.5
- M17 x 1.5
- M18 x 2.5
- M18 x 2.0
- M18 x 1.5
- M19 x 2.5
- M20 x 2.5
- M20 x 2.0
- M20 x 1.5
Contact
Wrong value, missing size, or supplier request? contact@tapandclearance.com