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H3, H4 Designation on Taps

H3, H4 Designation on Taps

H3, H4 Designation on Taps

We have 3 different sizes of tapped holes called out:

7/16-20 UNF-3B
3/4-16 UNF-3B
7/8-14 UNF-3B

On the drawing it calls out the hole geometry for each tapped hole per MS33649.

We have go/no-go thread gages per class 3B and we have the boring tools per Ms33649.  The taps do not have a 3B designation rather they have H3 for the 7/16 qnd 3/4 taps and H4 for 7/8 tap.

What is the H3 and H4 referencing and/or what does it mean?

Jesus is THE life,

RE: H3, H4 Designation on Taps

These are tolerance class for the taps themselves. Class 3H should generaly be suitable for class 3B female thread as per ANSI B1.1 Tap class GH5 for class 2B thread & so on.

If you want I shall post a link which gives some of this information. Maybe you can ask some tap manufacturer to give you a tap selection guide.

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