This bearing is a test piece for a home project. I want to build a working Stirling engine, and I need to get the friction down.The bearing uses 12, 4mm diameter, steel ball bearings which I got from my local cycle shop. Assembly is very , er... fiddly, but it is possible with a bit of patience.Place the shaft in the housing and add three bearings, jiggle it about to get the three balls in the groove. As you add more bearings you will need a screwdriver to 'click' them into the groove. 6 in the lower groove and six in the top. Glue on the end cap and pick up all the balls you dropped onto the floor while assembling ...