This is a linear bearing that works with 6mm airsoft bbs.
Print the stl, fill every hole with 3 bbs and then glue the cap in order to keep the bbs in place.
I've printed it in abs scaled up by 1% to prevent abs restriction and little error of printing, probably with good printer you can print in at natural dimension.
I've used normal plastic bbs and with some lubricant it works pretty good, probably it's better to use steel or ceramic bbs, I will try them as soon as possible.
NOTE: The external diameter is NOT the same as traditional 3d printer's linear bearing, it' exactly 23.32 mm.
I'm not anglophone so if you notice some errors in the text please leave a comment, thanks!
For the first print I've made a rapid test with 0.8mm walls and 0 infill, it turned out to be enough strong to be used.
-fill every hole with 3 bbs
-glue the cap without drain glue down the holes
It's reccomended to lubricate the bearing.