I've found it useful in terms of modularity, to be able to insert a capture nut in the place where a 608 ball bearing might be.This thing is a very simple cylinder with a capture nut indent. Otherwise, there is a thru hole the allow 5/16" rod to pass all the way through.It mates nicely with this thing: http://www.thingiverse.com/thing:5679Depending on your printer, it could be a very tight fit. I heat the receiver with a heat gun, and then press fit the captured nut bearing into the receiving hole.1) Look at your various objects that use bearings and determine if any piece can be reused by having a captured nut instead. 2) Print a few of these 3) Press fit a nut into the hexagonal recess of this thing. Works best as a press fit if you heat the thing and then press the nut into place (permanent connection) 4) Press fit the thing, which now has the captured nut, into the place that is the size of a 608 bearing. 5) Rejoice!