How to create a female taper thread?

[BaronJ]

Hi Guys,

Looking at picture 3, I would say that any taper on that thread has been the result of threading it into a partially threaded hole. In any case the taper on the nose would have to be pressed against a similar taper at the bottom of the hole. So a tapered thread wouldn't be necessary.

With regard to a nut. Since the hole at one end would be quite a bit smaller than the threaded part, a tap wouldn't fully form the threads towards the bottom, but would appear tapered because of the taper on the tap.

 

[Ca-g]

The pipe is 3/16 but both threads in the picture are 26 tpi.

 

[justintime]

The pipe is 3/16 but both threads in the picture are 26 tpi.

26 tpi pitch is quite possibly a 1.0 mm x ? dia. Can you confirm that thread OD ?
3/16 tube would be 4.75 mm ? ? If that is a Metric tubing size... ?

 

[deverett]

From the age of the lamp and its origin, I doubt that it will be a metric thread.

It is quite possible that the nut has been screwed and unscrewed quite a few times in its life and so the present diameter could well be slightly under the original. As has been mentioned before, the pipe end looks like a brake pipe type flare and so that will give the seal.

5/16" x 26 is a BSB thread.
Tubal Cain in his book The Model Engineer's Handbook, Third Edition gives 5/16" x 26 tpi tapping drill as letter K or 7.2mm for a 65% engagement.
So looks like the problem is solved!

Nice looking lamp, Chris. Deserves to be well treated.

Dave
The Emerald Isle