Of the brake bleeding type!!
Has anyone seen nipples so small?
18xm8 (x1.25 I think)
As the picture shows, not much thread makes it into the Nissin caliper so could go shorter.
Ignore the fact that it doesnt have the nipple head.

looks more like a house radiator bleed valve!

My eyes lit up when I saw this thread

Seriously though, I seem to remember that my Citroen BX had small ones like that on the rear calipers.

Hope not!
This picture shows them at bottom of caliper, nipple heads ground off otherwise wheels wouldnt go on.
Once Iv managed to get new ones, Ill bleed up then grind heads off to fit wheels, not ideal but cheaper than bigger wheels.

hahaha yeah I bet! figured it was a good way to get lots of views, thanks for that Ill investigate

You will get them on ebay the stainless ones are short enough on my calipers the hex is almost touching the caliper casting

Stainless Steel Bleed Nipple M8 x1.25: Motorbike Bleed Nipple Stainless Steel | eBay

thank you

"This picture shows them at bottom of caliper"
shouldn't the bleed screw go at the top of the calliper?

Just had a look at a Citroen BX rear bleed nipple.

Definitely M8 X1.25 thread, unfortunately it wouldn't be of any use to you as the plain section with the sealing area is about 10mm long
Looking at your's you probably wouldn't even manage to catch the first thread.

Got other small nipples here but I know they are all imperial threads

Im sure your right Gremlin but I can only work with what it came with. Its been a bugger trying to bleed them conventionaly, once I manage the correct nipples Il reverse bleed it.

Thanks for your efforts bonzoronnie.

tried swapping the calipers round, rh - lh and vice versa, worked a treat and bled right up. amazed they werent done like that originally. nipples were hard to find due to thread and total length but managed too. bled up then cut heads off so wheels would fit.