11-21-2015, 10:32 AM
Those bands are manufacturer specific. Some makers use colored bands as code for what materials the tap is engineered to cut.
What you have there is what we (here in the US anyhow) as being "series" or "serial" taps which are a series of three for progressively larger thread pitch diameter. What we do differently here is make all taps to a given "class of thread" (meaning thread pitch diameter limits) and it's one tap, one pass to finished pitch diameter.
When we find hand taps in sets of 3 here, it's three different lead styles. One with a long 6 to 12 pitch lead is a "taper" and serves to act as your series taps do by taking progressively more material as you wind it in. The second is a "plug" tap, with 3.5 to 5 leads of thread. It's the most popular, most common one if you buy just one tap. The third style is a "bottoming" tap with 1.5 to 2 leads of chamfer. It's used just as you think, to get threads as close to the bottom of a blind hole are possible. Typical application would be to use a taper or plug tap (rarely both in succession) to start the blind hole, then use the bottoming tap only to finish the last few threads. The pitch diameter for the bulk of the thread is already finished.
I've never really understood the need for those serial/series taps. One & done is how I use most every tap in my shop, and 99% of the time it's with high quality HSS, HSS-Co or HSS-PM machine taps.
You are probably using your correctly, though all you have to do for assurance is measure the O.D.'s of them.
What you have there is what we (here in the US anyhow) as being "series" or "serial" taps which are a series of three for progressively larger thread pitch diameter. What we do differently here is make all taps to a given "class of thread" (meaning thread pitch diameter limits) and it's one tap, one pass to finished pitch diameter.
When we find hand taps in sets of 3 here, it's three different lead styles. One with a long 6 to 12 pitch lead is a "taper" and serves to act as your series taps do by taking progressively more material as you wind it in. The second is a "plug" tap, with 3.5 to 5 leads of thread. It's the most popular, most common one if you buy just one tap. The third style is a "bottoming" tap with 1.5 to 2 leads of chamfer. It's used just as you think, to get threads as close to the bottom of a blind hole are possible. Typical application would be to use a taper or plug tap (rarely both in succession) to start the blind hole, then use the bottoming tap only to finish the last few threads. The pitch diameter for the bulk of the thread is already finished.
I've never really understood the need for those serial/series taps. One & done is how I use most every tap in my shop, and 99% of the time it's with high quality HSS, HSS-Co or HSS-PM machine taps.
You are probably using your correctly, though all you have to do for assurance is measure the O.D.'s of them.