5/16" bolt and 7/8" ball bearing
Front bearing and bolt
Back bearing and washer spacer
this is a 2 x 4 and install 2 ball bearings one in front and one at the back, both bearings have to be parallel and inner bearings connect by the bolt and can not contact the wood that will reduce the movement. outter bearing should tie fit to contact 2 x 4. front bearing direct contact bolt and the back bearing connect with one washer just large enough to contact inner bearing. see the third picture. this set up makes the turning smooth.
in Jan18, all these targets will be in play for CAPS first shooting. ardo, if you want, come by check it out.