[How-To] Tap styles and their uses?

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Brento

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I just got a bunch of taps from @mattthemuppet2 I got a thread forming style tap and then i got some self thread locking taps. What be some good uses for a thread forming tap vs a regular tap and what are some good uses for the self thread locking taps?

Another note. I have a 3/8-16 tap that seems large for its size. It isnt an sti tap but it does say DTC on it. Anyone here of that style tap before. I would just like to know so i can try and catalog it and not grab it on accident.
 
Self thread locking would be good for vibration prone environments. I'm going to go through my pile and dig out any I have. They'd be excellent for stuff I make for my bicycles, that's a pretty harsh environment for fasteners
 
I am by no means conversant with taps, and even less so of moderm terminology. So anything I say can be corrected later when a real expert comes along.

As to your first question about 'thread forming' taps, I take that to mean that the tap displaces the outer diameter of the hole to form the innermost portion of the thread. The key thing here is that the tap drill is much larger than a thread 'cutting' tap.

About the 3/8-16 tap, there are taps for thread inserts that when installed become the correct size. I don't know what all the abbreviations are for, just that I have a tap marked 1/2-20 that is sorely over sized, nearer to 9/16, that is for thread inserts.

I don't remember the brand of the inserts, just that the taps are packaged along with the inserts and marked for the finished size. It could very well be what you have. The dimensions of the insert are very slight.

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Brento said:
I just got a bunch of taps from @mattthemuppet2 I got a thread forming style tap and then i got some self thread locking taps. What be some good uses for a thread forming tap vs a regular tap and what are some good uses for the self thread locking taps?

Another note. I have a 3/8-16 tap that seems large for its size. It isnt an sti tap but it does say DTC on it. Anyone here of that style tap before. I would just like to know so i can try and catalog it and not grab it on accident.
Click to expand...
Maybe the attached will help?
 

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It does sorta. Thread forming is good in plastics basically. So has anyone used the thread locking style taps before?
 
Brento said:
I just got a bunch of taps from @mattthemuppet2 I got a thread forming style tap and then i got some self thread locking taps. What be some good uses for a thread forming tap vs a regular tap and what are some good uses for the self thread locking taps?

Another note. I have a 3/8-16 tap that seems large for its size. It isnt an sti tap but it does say DTC on it. Anyone here of that style tap before. I would just like to know so i can try and catalog it and not grab it on accident.
Click to expand...
Forming taps are best used in malleable iron or softer nonferrous alloys like aluminum and brass. As mentioned, they displace the material rather than cut threads. I've used several sizes over the years. Also as mentioned they require a larger pilot drill than a thread cutting tap. There's a formula in the Machinery's Handbook for determining the size of hole needed.

As for the oversize tap, does it have an H rating engraved or etched on the shank? The letter H followed by a number indicates how much larger an imperial the tap is over the nominal size. Each number represents an increase of .0005" over the nominal. For instance, a 1/4" tap marked H3 is .0015" larger than the nominal .250", or a final size of .2515". H2 and H3 are the most common sizes used for tapping holes in material that doesn't need to be plated. Standard H limits go up to H12 or .006" over the nominal size of the fastener to be inserted. The larger sizes are generally used when the final product needs to be plated. Different plating materials leave different thicknesses of deposits thus the range of oversize taps.

Metric taps a similar identification marking using the letter D rather than the letter H.
 
Is it possibly a 3/8" pipe tap? they are 18tpi rather than 16 tpi.
 
Nope not pipe. Id be able to tell them plus i checked the pitch and i could just read the size on the shank.
 
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