This is a great motor w/ encoder. It is nearly silent but provides good power. The output is a through-hole which is two squares offset by 45 degrees. The squares are just less than 1/4'. We were able to broach one of the squares to 1/4 and it now fits Vex high-strength axle very well. This is a handy (and FRC-legal) way to drive Vex mechanisms if you need something small but don't want to use servos.