I think i know the one youre talking about. About 6mm in diameter and about 8mm long :?
Dont hold m e to this but maybe :? and it might be a while as its the type of thing ends up in the very bottom
Just had a thought
Those plastic jubilee clips of the type seen on cheap bike mounted components is very very similar :? Well one component part of it is and if you remove the cable that plastic screw falls out. Cant say for sure but you might find different sizes.