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I've come across this at work, but no one here has seen the like before.
It's a slotted spring pin, but it has the extras on the slot, that'll engage when the pin is pressed into the hole.
It's approx 18mm od.
It's a galvanised Doofer .
or giant roll pin with keys to stop it twisting when you smack it in an ole 🙂
Toothed spring pin or roll pin
https://www.huyett.com/blog/introduction-spring-pins
fasthaggis
Full Member
or giant roll pin with keys to stop it twisting when you smack it in an ole
Yup, seen things like that in different shapes n sizes over the years e.g. some wee ones

Flanged pin-thruster.
HtH
An 18mm pin punch would be something to behold.
Thanks for the link, sharkey.
So, it looks like we need to find a toothed split spring pin... A ****in' big one.
Thanks, folks (can I say that?).
Differential gurdle spring I think
3/8ths gripley is it not?
Fast haggis has it... the slots allow you to "flog" it out with big punch and a big hammer without it twisting.
Roll pin. I posted something like this a while back. My was in a shredder/chipper.