Had a look around for it, couldn't find the damn thing. All of my screenprinting stuff is in storage while I renovate my garage, I think it got lost in the move.
Basically, it's the most low-tech thing in the world

I got a chunk of wood, shaped it into a rough sleeve shape (was only doing a run of 5-10 shirts with the print, thought I may need it again though). Drilled a hole into my (wooden) platen, self-threaded it using a bolt. Proceeded to cut head off bolt, glued it into my "sleeve" block of wood. Then after it dried, I could sort of screw it in and out.
Obviously not a permanent solution, nor a smart one, as I imagine after 5-10 screw/unscrew cycles the thread is going to give way or the bolt is going to detach itself from the sleeve half. Or, I guess, I lose the sleeve pattern as has happened in this case.
I would think a more permanent solution isn't too far off track from what I have done. If I ever need it in the future I'll engineer something better and post a guide
