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.
7/8-14 Tap Drill Size and Clearance Hole
- Tap Drill: Soft Matl.
- 13/160.8125"
- 75% Thread Engagement
- Tap Drill: Hard Matl.
- 53/640.8281"
- 50% Thread Engagement
- Clearance: Close Fit
- 57/640.8906"
- Clearance: Free Fit
- 29/320.9062"
Related sizes
About the 7/8-14 thread
7/8-14 is a UNF (Unified National Fine) thread with a 0.8750" major diameter and 14 threads per inch, giving a minor diameter of 0.7874". In aluminum, brass and plastics, drill 13/16 (0.8125") for about 75% thread engagement. In steel, stainless and cast iron, step up to 53/64 (0.8281") 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 7/8" screw to pass through, drill 57/64 (0.8906") for a close fit or 29/32 (0.9062") for a free fit.
7/8-14 tap drill options by thread percentage
| Drill | Decimal | Thread | Use |
|---|---|---|---|
| 51/64 | 0.7969" | 84% | |
| 20.25 mm | 0.7972" | 84% | |
| 20.5 mm | 0.8071" | 73% | |
| 13/16 | 0.8125" | 67% | Soft matl. |
| 20.75 mm | 0.8169" | 63% | |
| 21.0 mm | 0.8268" | 52% | |
| 53/64 | 0.8281" | 51% | Hard matl. |
Form (roll) tap: drill 27/32 (0.8438") 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