need info on brake caliper pistons size

[lingeringstin...]

I need pair of disc brake pistons. I'm intending to use them as lower spring cups for my sprung saddle and the springs I want to use are 30mm diameter cylindrical compression springs that look like giant valve springs.

The brake pistons would be bolted to my bike frame via a drilled bolt hole down the middle. The springs would sit in these cups so they won't wander about when in use.

Doesn't really matter what the external diameter is but I need the internal depression part of the pistons to be at least 30mm diameter. Type of metal doesn't matter.

So what brake pistons have an internal diameter of 30mm or a little more?

...................

RD250 ones look almost rght but are just a bit too wide I think and probably not cheap. I'm finding Land Rover Defender ones for just over a fiver that might be close and Triumph ones for like Herald or something look close. I'd prefer ally ones (Brembo etc.) but whatever I can get will do.

[sickpup]

Would be a lot cheaper to buy some 34mm tube with 1mm wall and weld a bottom to them.

[WD Forte]

I agree with Sickpup that making some out of tube/plate would be less of a faff.
but IIRC, early Honda CX500 bikes circa 1979/1980 used a single 38mm or 42mm caliper so I might look into those for starters
The 38mm could have an internal diameter not much over 30mm.
IIRC again, some aftermarket ones came in nice shiny Stainless too.

There ya go, I googled it for ya
a 38x35 caliper, you just need to check the wall thickness
but I don't recall them being super thick


https://www.ebay.co.uk/itm/272269928057?
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bikers smell of wee

[lingeringstin...]

Cheers for that info. I can probably find some of them at a breaker's yard for nowt. For now I found some 1" brass end caps in my pile of shite that will do until I get something else.