The Factorio locomotive made into a keychain! each piece is ~33mm long with the holes in the center being 2mm across
No oil taker yet but I am working on it!
I used 7 strand steel beading wire. to thread through the pieces then leaving a little under the length of the last wagon extra to loop back into opposite holes. I jammed a piece of copper wire in to keep it from pulling back out and put a nice gob of super glue on the back to keep it from pulling out.
The length is basically as long as you want it to be.
I added the Raw model without holes for those making minis (the bottom isnt totally flat)