This part is the same width as the extruder carriage (62 mm), is (14.5 mm thick)
it fits snugly in the space available inbetween the bearings (20 mm high).
Mounting holes are 4x5 mm elliptical to have a little room for movement.
2 top holes - 53mm apart, 2 bottom holes - 40mm apart, screw onto the carriage with 18mm M3 bolts. The 6 mm belt just slides in the (10mm x1mm wide) groove and needs no further fastening.
designed specially for my chinese anet a8 PRUSA i3 with an acryllic 8mm frame, wich came to me with no recognisable belt connector in the box, so after some time with an improvised setup i designed a one that does the job a lot better. A litte room for movement with the screws in eliptical holes for mounting it.