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Taper, Plug and Bottoming Taps: How to Use a Hand Tap Set

Guide · Updated October 28, 2026

Hand taps come with three standard chamfers. The chamfer spreads the cutting load over several teeth: the longer it is, the easier the tap starts, but the farther from the bottom of a blind hole the full threads stop.

Check the tap drill hole

Measure the drilled hole before tapping. The free Gage Block Calculator builds the stack.

Step by step

Know the chamfers: Taper: 7–10 threads. Plug: 3–5 threads. Bottoming: 1–2 threads (Fastenal, Kennametal and MSC tap data).
Through holes: A plug tap alone is usually enough; a taper tap is easier to start in hard material or thin walls.
Blind holes: Start with a taper or plug tap, then finish with the bottoming tap.
Drill deep enough: Drill deeper than the full thread so chips have room.
Lubricate: Use tapping fluid suited to the material.
Clear chips: Back the tap out and clean chips before switching to the bottoming tap.
Finish gently: The bottoming tap takes more torque; feel for the hole bottom.

Worked example: blind 1/4-20 hole

P = 1 ÷ 20 = 0.050 in. A plug tap with a 4-thread chamfer has its first full thread 4 × 0.050 = 0.200 in from the tip, so a plug tap run to the hole bottom leaves about 0.200 in of partial threads. A bottoming tap with a 1.5-thread chamfer leaves about 1.5 × 0.050 = 0.075 in. If you need 0.375 in of full thread, drill at least 0.375 + 0.075 = 0.450 in deep plus room for chips and the drill point, and use the bottoming tap last.

Naming: US vs UK

Wiseman Threading Tools notes that in the UK a "plug" tap often means the bottoming tap, while in North America "plug" means the 3–5 thread second tap. Order by chamfer count or use taper, second and bottom to avoid confusion.

Chamfer angles

ISO 529 hand taps: taper lead about 5° per side, second about 8°, bottom about 18° (Wiseman). Steeper chamfer means fewer teeth share the load and more torque.

Common problems

Broken bottoming tap: started a bottoming tap in a fresh hole or packed chips at the bottom. Short thread: hole not drilled deep enough. Crooked thread: no guide.

Tips

Straight: start a tap straight.
Wrench: tap wrench.
Drill: tap drill chart.

FAQ

How many threads of chamfer on a taper tap?

7–10.

Plug tap chamfer?

3–5 threads.

Bottoming tap chamfer?

1–2 threads.

Can I start with a bottoming tap?

Not recommended; start with a taper or plug tap.

Which tap for through holes?

A plug tap is usually enough.

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