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+--- Thread: Rad drain tap hole thread (/showthread.php?tid=7161)
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RE: Rad drain tap hole thread - Steve Bryant - 11-02-2022
That could well be a possibility Ruairidh.
RE: Rad drain tap hole thread - Ruairidh Dunford - 11-02-2022
That is why several of us suggested it to you.
RE: Rad drain tap hole thread - Steve Bryant - 11-02-2022
To my knowledge the rad is as made originally so I would have to think that the hole and threads are as originally made also. Probably the best plan of action would be to turn up a thread cleaning tap to match the thread form and TPI and diameter of the drain tap and carefully run that through the hole until the correct fit is achieved.
RE: Rad drain tap hole thread - Bob Culver - 11-02-2022
Nothing is impossible. Radiator and the various cocks could be various threads, including 1/2 UNF. TPI can usually be established with care. A taper tap run through will cut too large for a parallle fitting.
RE: Rad drain tap hole thread - Reckless Rat - 11-02-2022
Have you not got one of these?
![[Image: hand-mechanic-man-holding-thread-260nw-1306901428.jpg]](https://image.shutterstock.com/image-photo/hand-mechanic-man-holding-thread-260nw-1306901428.jpg)
Even if it won't fit inside you can take a cast with plasticine or silmilar
Photo shows a metric gauge but you'll need an imperial one.
RE: Rad drain tap hole thread - Steve Bryant - 12-02-2022
Reckless, thanks for the suggestions. Yes I have several thread gauge sets, but you gave me a great idea about taking an impression from the hole itself so that I can check the TPI then make a cleaning tap to do the honors.
Stephen
RE: Rad drain tap hole thread - Hugh Barnes - 12-02-2022
and perhaps check that it's the same thread as the drain tap....
RE: Rad drain tap hole thread - Steve Bryant - 12-02-2022
I'm hoping it is Hugh.
RE: Rad drain tap hole thread - Dennis Nicholas - 13-02-2022
Another possibility is to use soft wood dowel screwed into the hole to get the thread size/type
RE: Rad drain tap hole thread - Bob Culver - 13-02-2022
I have found it more convenient to count hthreads in say 1/4 inch using the ever handy vernier gauge.
Probably not applicable here but poor threads can sometimes be improved by sawing slots in a bolt, preferably tough stuff, as a tap.
From various sources charts are availablae of threads in progressive sizes with tpi/mm pitch, tap sizes etc. Very helpful for identity and for figuring remedies.