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SHEET FA-TD-1-4-20 · CUTTING TAP · INCH SERIES
1/4-20 tap drill size
Cutting-tap reference · 1/4-20 UNC
RECOMMENDED TAP DRILL
#7
Ø 0.2010 in
Ø 5.1054 mm
mm converted at 1 in = 25.4 mm
- NOMINAL Ø
- 0.25 in · 6.35 mm
- THREADS / IN
- 20 TPI
- METHOD
- CUTTING TAP
- CHECKED
SECTION A–A · DIAMETERS TO SCALESCALE 20:1
Dimensional comparison only. Not a substitute recommendation. Figures in mm.
NOTES
- Cutting-tap reference for aluminum, brass and plastics. The source column is headed 75% Thread; this is a chart category, not a calculated or guaranteed engagement for this row. Its steel, stainless steel and iron column instead lists 7/32 under 50% Thread. Confirm the final hole size with the tap maker for the material, thread class and hole depth. Not for forming taps.
- Forming taps require different hole guidance and are not covered here.
- Converted figures use exactly 1 in = 25.4 mm; source precision is preserved separately.
Source precision: 0.2010 in. Thread: 1/4-20 UNC.
SOURCE
Manufacturing Processes 4-5 — Unit 5: Tapping, Archived 2026-04-15; accessed 2026-09-09, Unit 5: Tapping, Tap & Clearance Drill Sizes, table1.png, 1/4-20 row, aluminum/brass/plastics column; bd_warehouse Soft cross-check, checked 2026-09-09.
Adapted from Unit 5: Tapping, LamNgeun Virasak, Open Oregon. CC BY 4.0: https://creativecommons.org/licenses/by/4.0/ . Selected rows; wording adapted.
Verification method →