Tandem Headset: 1 1/8" threaded type: tpi?

[Ross K]

My 1992 Galaxy Twin Tandem needs a new headset.

I've not dismantled it yet but the quill stem (an ugly, clunky-looking angle-adjustable type) seems to measure 25.8mm by my vernier calipers, at the top of the stem where it disappears into the top headset locknut (it's slammed down quite far), so I presume the "actual" diameter of the stem is 25.4mm.

Looking at Sheldon Brown's crib table ( https://www.sheldonbrown.com/cribsheet-headsets.html) I need a 1 1/8" threaded headset with 26tpi threads.

I see that SJS list a load of 1 1/8" threaded headsets but I cannot see the tpi data listed on any. I also note that 1 1/8" threaded headsets are offered by eBay sellers in a choice of 24tpi and 26tpi.

So I'm a bit confused! I presume my steerer tube is 28.6mm outside diameter but will the threading be 26 or 24tpi?

By the way I've read this 2012 thread but it doesn't seem to offer the answer. viewtopic.php?t=102045#p959926

[Brucey]

26tpi is the default thread pitch in this size. I don't think I've seen 24tpi in fact.

If you want to check the pitch for yourself, you can use a thread pitch gauge or alternatively you just need an example of both 26tpi and 24tpi male threads that can be offered up alongside the steerer. So for example a BSC threaded axle (26tpi) and a BSC threaded BB cup (24tpi). One will 'mesh exactly' with the steerer threads, the other won't.

cheers

[Ross K]

26tpi is the default thread pitch in this size. I don't think I've seen 24tpi in fact.

If you want to check the pitch for yourself, you can use a thread pitch gauge or alternatively you just need an example of both 26tpi and 24tpi male threads that can be offered up alongside the steerer. So for example a BSC threaded axle (26tpi) and a BSC threaded BB cup (24tpi). One will 'mesh exactly' with the steerer threads, the other won't.

cheers

Thank you Brucey, much appreciated!