Pick the tap drill for your thread in seconds. Choose metric (M) or inch (UN/UNC/UNF), set a target engagement (e.g., 60–75%), and get the suggested drill size with cut vs form tap notes, letter/number alternatives, and quick export. Ideal for CNC machining, prototyping, and shop floor setup sheets.
Select thread → e.g., M6×1.0, 1/4-20 UNC, 10-32 UNF.
Set target engagement (typical: 65–75% for general work; use 55–65% for small taps/hard materials).
Click Calculate → copy the drill size (mm or inch), check alternatives and tap type notes, then Get a Quote.
Recommended drill for your target engagement, plus two nearby options
Tap type note (cut vs form tap) and material caution (brittle plastics, HRC steels)
Alternatives: metric mm, fractional inch, letter and number drills
M6×1.0 @ 70% → 5.1 mm (alts: 5.0 / 5.2 mm)
M8×1.25 @ 65% → 6.8 mm
M10×1.5 @ 70% → 8.5 mm
1/4-20 UNC @ ~70% → #7 (0.201 in)
10-32 UNF @ ~70% → #21 (0.159 in)
5/16-18 UNC @ ~70% → F (0.257 in)
Tip: For form taps, use a larger drill (lower engagement) vs cut taps to keep torque down. For brittle plastics, avoid high engagement.
Mini Notes (keep it practical)
General-purpose: 60–75% engagement suits most jobs.
Small taps / hard materials: try 55–65% to reduce tap torque and breakage.
Form taps: require bigger pre-drills than cut taps for the same nominal thread.
Plastics: Delrin/ABS machine well; nylon absorbs moisture; acrylic can crack → lower engagement, sharp tools, good chip evacuation.
Thread: e.g., M6×1.0 Target engagement: 70% Tap type: Cut / Form
Recommended drill: 5.1 mm
Alternatives: 5.0 mm (higher engagement) | 5.2 mm (lower torque)
Notes: For form taps, start at 5.2 mm; for brittle plastics, avoid >70% engagement.
Q1. What engagement should I choose?
For everyday work, 60–75% is common. Use the lower half for small taps or tougher materials to reduce torque.
Q2. Cut tap vs form tap — which drill size?
Form taps need a larger drill (lower engagement) than cut taps for the same thread. Start ~1 step larger and test.
Q3. I only have letter/number drills — can I still match?
Yes. The calculator lists fractional, letter, and number equivalents where applicable.
Q4. Plastics and thin walls?
Use lower engagement and sharp tools; keep heat down. Some plastics (e.g., acrylic/PMMA) crack easily — consider thread inserts.
Q5. Can you quote my parts with these threads?
Yes. Click Get a Quote and we’ll pre-fill your thread and drill choices; add quantity/material/finish for pricing and lead time.
