View Full Version : Hand Tap Chamfer Specs?

Paul Alciatore
02-27-2013, 01:29 PM
I am doing some research on taps, mostly on hand taps at the present time. Hand taps are often sold in sets of three: taper, plug, and bottom. The main difference in these three taps is the length and angle of the tapered area at the tip, properly called the chamfer. I can find specs for every other dimension on hand taps down to the fifth decimal place, but can not find even a general rule for the length of these chamfers.

The best reference I can find for this information is the McMaster-Carr web site which, in summary, states:

Taper Chamfer = 7 to 10 threads
Plug Chamfer = 3 to 5 threads
Bottom Chamfer = 1 to 2 threads

Is there any better spec on the lengths of these chamfers? Perhaps a manufacturer's site?

I may be looking at spiral point taps next so any info on them would also be appreciated.

02-27-2013, 09:02 PM

Paul Alciatore
02-27-2013, 10:11 PM
Good one. It says about the same thing as McMaster. It is nice to see confirmation.



02-27-2013, 10:28 PM


Black Forest
02-28-2013, 01:47 AM
Not related to your inquiry directly but a heads up for those that don't know this little bit of info.

I bought a set of taps and dies in a nice plastic case a few years ago. There were three taps of each size included. Wow I thought. I just grabbed one of the three taps for what ever size I needed. Damn taps were crap. Half the time the bolt wouldn't thread into the hole or the tap broke. I was surprised as these taps were made in Germany and not a cheap Chinese import. Then Lo and Behold I found out on this site that Hand taps often come in a set of three. You use the tap with one ring on the shank first. Then the tap with two rings and finally you finish the hole with the tap with no ring.

All of a sudden my crap taps were fine at cutting on size and didn't break! I then went and bought machine taps of all the sizes I needed. Live and Learn.

Sorry for the hijack but it might save someone some head scratching and money.

Paul Alciatore
02-28-2013, 02:17 AM
Yes, a few years ago I got a set like that myself from Grizzly. It was a set of metric taps. I had many hand taps that I had purchased at various times over the years and all of them, weather hardware store, or ground taps in sets of three (taper, plug, and bottom) cut a full diameter thread. But these metric taps from Grizzly were marked with 2, 1, or no rings and a close observation showed that not only were the chamfers of different lengths, but the ones with 2 rings only had about 50% of the full tooth height and the ones with 1 ring about 75% of the tooth. A screw would not fit in a hole that was threaded with only the 2 ring tap or even in one threaded with a 1 ring tap. You had to use all three of them in succession to get the full thread. This system has it's advantages and disadvantages. Since each tap only cut a fraction of the thread, there is a lot less danger of breakage. But it takes three times as long to get even a through hole threaded.

I concluded it was a metric thing. I have never seen or seen a description of such taps in English (inch) sizes.