This is the lead nut used for the eShapeoko Z axis (when using the M8 threaded rod). It is made of black acetal (Delrin). It has one M8 x 1.25 hole (for the threaded rod) and two M5 x 0.8 holes at 20 mm centres (for mounting). The overall dimensions are 35 mm x 20 mm x 13 mm.
The nut fits between MakerSlide and a carriage plate, if the wheels are mounted using the standard eccentric spacers on the side of the wheel, plus two washers each. The fixed wheels need a 6.35 mm spacer and two washers each.