This is a belt idler guide for 13mm bearring that will fit on most 3d printer. I found out that the belt tends to grind on the edge of the tensioner/idler and this is not a good idea to leave it grinding at the edge. It might break the belt one day and the benefits of adding this little friend you will get smoother and lighter motion while lessening the friction caused by the grinding at the edge

The plastic were grinded on the edge of the bearing holder, it might generate a lot of plastic particles

Printed mine with these parameters

ABS
layer 0.1
bed 110c
extruder 230
speed 20mm