Ender 3 tensioner - uses stock bearings and screw

thingiverse

Thanks to MakeChetti's remix! Using bearings makes sense because without them, increasing belt tension only increases movement resistance. With bearings in place, you can apply as much tension as needed without any hindrance to movement. Tighter belts also mean more accuracy, and I think that upgrading your Ender 3 with bearings is a vital improvement.