Just one small nick on a pinion can eventually destroy a plastic spur gear! With that in mind, RPM designed this case that holds each pinion on its own post and the lid snaps shut, so there is no need to tighten the set-screw to hold the pinions in place! With each gear locked in its own place, never touching any other gear, you are assured of perfect pinion gears, no matter how knocked around the case may get in your toolbox!