Fits all 20mm to 28mm brushless motors with 2 or 4 bolt mounting pattern on face (99% of everything ever made?). This is a heavy duty box (up to a Hacker B-40). Fits traditional 10mm x 10mm stick mounting box, fits most planes designed with GWS gearboxes also. Output shaft is a stout 4mm. Comes complete with aluminum prop adapter and mounting screws. Choose from popular gear ratios below. Included pinion is 2.0 mm bore. Other Pinion sizes and bores available in Gearbox Parts (a subcategory of the Gearbox category your in now). Notice that since the motor may be pivoted for gear lash adjustment that many other ratios may be attained with other pinions and spurs. Rugged 4mm shaft works with all GWS EPS 400 spur gears (Listed in "Brushed Motors" sub category "GWS Motor System Parts") for an even wider range of gear ratios than stock listed below.