English French German Italian Spanish

Tank tap thread question

Submitted by christian_wyss on Mon, 17/07/2023
Forums
Nortons - General

Sorry it's not for a Norton but I thought I might get some help over here.

Looking for a tap and die set, I am wondering what to order. Diameter looks close to 1/2", in fact 12,5mm, and the beginning of the thread looks like 24tpi. But it isn't. Have a look  at the photos.

 

What do you think?

Attachments
Tap.jpg
24tpi looks good... .jpg
But isn't... .jpg

Submitted by mikael_ridderstad on Mon, 17/07/2023

Permalink

It might be BSB (British Standard Brass) 1/2" o/d, 26 tpi.

If it is for something British.

Submitted by david_cooper on Mon, 17/07/2023

Permalink

Norton tank threads (and often others) are 1/4" BSP.  Which is 19tpi. Google dimensions. The OD  is just over 1/2".

Pipe thread nominal size (1/4") refers to the internal size of pipe. It's still in common use today.  Thankfully (or house maintenance would be ever more complicated).

Submitted by robert_tuck on Tue, 18/07/2023

Permalink

Looks just  like the thread on the Norton tap,  as above 1/4  BSP  .  Most confusing to many  as it measures so much bigger than that. I have a whole range of BSP taps, where are you based ?.

Submitted by christian_wyss on Tue, 18/07/2023

Permalink

Looks like we also have some of them over here. It's about an 1930 Alcyon with one metric and one British tap on the tank. They had AMAC carbs in that time, which could explain half of the situation.

Thanks but it looks like OD is a little bigger than the tap OD thread I have (12,5mm), for a tap I believe it would do it. But 19 TPI is not fine enough I think.

Attachments
Ryco.jpg

 


Norton Owners Club Website by 2Toucans