Machinist Tap Drill Chart

Tap drill, clearance hole, roll-form and STI sizes for UNC, UNF, metric, NPT and BSP — with the percent of thread the drill really gives you.

The chart on the shop wall says 1/4-20 takes a #7. It does not say what thread you actually end up with.

This one does. Pick a thread and it names a drill you can pick up out of the index — then shows the diameter the formula asked for, the difference, and the percent of thread that drill really cuts. You asked for 75%. The #7 gives you 75.4%. Both numbers are on the screen, because the second one is the one in your part.

WHAT IS IN IT, FREE

• Cutting taps: UNC, UNF, metric coarse and metric fine
• Forming and roll taps, on the forming constant rather than the cutting one
• NPT pipe threads
• Percent of thread at 60, 65, 70, 75, 80 and 85
• Fractional, number, letter and metric drills, cross-referenced against each other
• Search, and the nearest drill with its actual percent — on every thread in the app

WHAT PRO ADDS

• Clearance holes in close, free and loose fits
• STI holes for wire thread inserts
• UNEF, NPTF, NPS, and the British threads BSPP, BSPT, BSW and BSF
• Any percent of thread from 50 to 85, not only the six presets
• Saved threads
• Narrowing the nearest drill to the drill sets you actually own

HOW IT BEHAVES

Set the percent of thread and the drill follows it. Every result carries the formula it came from, the constant, and the name of the convention that constant belongs to, so you can check the number instead of trusting it. Switch between inches and millimetres and the thread you were looking at stays selected. Type a designation — 1/4-20, 10-32, M6, 1/2 NPT — and it is found however you write it.

It opens on a result. No splash, no tour, no sign-in.

Searching, the drill cross-reference, and the nearest drill with its actual percent are free on every thread the app knows — including the ones only Pro can compute a hole for. Nothing that tells you how honest a number is sits behind the paywall.

Pro is a one-time purchase. There is also a weekly subscription for anyone who would rather not pay for it all at once.

SUBSCRIPTION TERMS

Pro Weekly is USD 1.99 per week, charged to your Apple Account at confirmation of purchase, and renews automatically unless it is turned off at least 24 hours before the period ends. Manage or cancel it in your Apple Account settings. The one-time Pro purchase is USD 5.99 and does not renew.

Privacy: https://signet.co.jp/tap-drill-chart/privacy Terms: https://signet.co.jp/tap-drill-chart/terms

NO NETWORK

Every number is computed on the phone from tables shipped inside the app. There is no account, and it works with the phone in a drawer.

Drill sizes are a starting point, not a specification. What a tap actually produces depends on the material, the tap, the coolant and the machine. Prove it in scrap before you cut the part.