View Full Version : H2 or H3 taps?

Tony Ennis
07-09-2010, 07:12 PM
I'm buying a tap and have the choice of H2 or H3 thread limits. I read the definitions of them, but I didn't figure out which I actually want, lol.

Any suggestions?

07-09-2010, 07:14 PM
I believe H3 is standard thread, 2B fit

07-09-2010, 07:15 PM
gh3 is common, it works for most stuff fix it guys deal with.

07-09-2010, 07:48 PM
The H number is the number of half-thousandths the tap is oversize; there needs to be some clearance, or you couldn't screw the bolt in. So how much clearance do you need?

Generally, it depends on the thread size. For a 2-56 you might typically want an H2 or even an H1. For 1/4-20, maybe H3.

I generally choose what is highlighted as "typical" in the tool catalogs; I don't know enough to really judge H numbers myself.

07-09-2010, 09:37 PM
The H limit can also increase with diameter,larger taps can run H4 or H5.

Also if the part in question is intended to be plated or anodized selecting a higher H limit tap allows for clearance lost to the coating thickness.Apparently most aftermarket Motorcycle chrome bangers don't know this as I have an endless stream of weekend bike mechanics coming in with stripped threads and crossed blots.