This is a roller handle for crankwheels. i designed it to use a 1/4-20x3" bolt, but will work with whatever will fit through a 608 bearing (~8mm). Length wise it willneed to be longer that about 2 5/16" (67mm) just to make it through the body and nut.

you need

2 608 skate board bearings

1 bolt matching your handle thread (up to 8mm, or 5/16" in diameter and about 77mm or 3" in length, this will depend on the thickness of your jam nut and handwheel thickness)

1 matching nut

2 washers (under 18mm or ~5/8" just so it doesnt contact the outside rim of your bearing)

I have also added a sleeve that adapts a 1/4" bolt to the 8mm bearings to keep it centered. this ended up being very tight on a 1/4" bolt, i need to figure out a better design

I printed with 6 walls and 35% infill, should be more than enough strength