Small Taper Thread Tap

27 is a plain old pipe tap , so not sure why that one is so expensive , other than being Carbide . Jake could be correct as some taper taps are denoted with an S , for special . The " model shop " I worked in had all kinds of weird ass different pitch taps . Most were for gun making and I'm sure this was done on purpose by the engineers .
 
Most taps are broken down into three types... bottoming (fewest threads chamfered to get as many threads deep), plug taps (a few more threads used to cut the full thread), and taper taps, which have maybe twice the number of threads to cut a full thread.

A taper tap is great to start hand tapping a hole.

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Jake M said:
Me neither. :cool:


Speculating, and given the long taper....

I wonder if it's a "model making" special thread. They use a lot of threads that are much finer than "normal" ones, for better engagement over shorter distance. (Thinner work pieces). 32 and 40 are ones I've heard to be common.

1/16 is a valid pipe thread size in most if not all flavors, including tapered. Very uncommon in "the real world", but model makers use it. I wonder if you have a way to compare the taper. NPT threads are all tapered by 3/4 per foot, which is 1/16 per inch.
Click to expand...


Definitely a special tap and not a pipe tap.

Gun smithing or model making as mentioned are both distinct possibilities.
 
That price is ridiculous, they may be commonly bought for a tiny fraction of that price. I used that size with 27tpi on a product that I sold in my business on an item for checking the pressure (or lack thereof) in a wine bottle with a cork driven in; if this results in significant pressure in the bottle, leaks past the cork can be the result, with unsightly mold under the foil finish.
 
I'd love to ask @Bi11Hudson, but it looks like he hasn't posted since Jan 2023!
 
Never heard of a pipe thread hole in smithing, at least not for anything in the last 100 years but who knows...
How would one drill a tapered hole for this tap? Tapered end mil?
 
tobnpr said:
Never heard of a pipe thread hole in smithing, at least not for anything in the last 100 years but who knows...
How would one drill a tapered hole for this tap? Tapered end mil?
Click to expand...

You would drill a straight hole and then if you needed a taper use a tapered reamer.

Most people do not drill a tapered hole when using a tapered pipe tap they just let the tap enlarge the hole as needed so that the full thread is formed. If the hole were tapered and the thread profile had flat tops it would never seal.
I do have a set of tapered reamers for use with pipe taps to make the taping force less. But you do have to be careful to not make the hole to big where you do not get the full thread form.
 
This is a related post about oddball threads that don't match any standard. The answer I got from Starrett when I wanted to make a post for my #196 Back-Plunder indicator (a custom PT13820 rod) was:

"Here is the way it is spec’d.​
".231-28 Thread​
"Some of these items have been around so long, there weren’t standard threads. If we change them, they won’t fit the old tools."​

A 12-28 would be 0.216", and 1/4-28 would (obviously) be 0.250". My solution was an adjustable round 12-28 die, opened up to suit the 0.231" diameter rod end.

So in the case of older tooling, models, whatever, someone used whatever seemed right, and it perpetuated.
 
How old might the tap be? The old 'screw plate' tapping apparatus generated indeterminate
diameter fasteners, it was normal for taps in the 1800s to be tapered; you'd tap the nut deeper
until it fit to the screw.
 
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