Yamaha Marine Outboards Factory Service / Repair/ Workshop Manual 225G 250B L250B, Page 205Get this manual
SHIMMING (REGULAR ROTATION MODELS) (EXCEPT FOR USA AND CANADA)
(2) Calculate the reverse gear shim thickness (T2)Reverse gear shim thickness (T2)21.0R100 A100 M5 NOTE: "R" is the deviation of the lower case dimension from standardIt is stamped on the trim tab mounting surface of the lower case in 0.01-mm units If the "R" or "A" mark is missing or unreadable, assume "R" and "A" value of "0", and check the backlash when the unit is assembled If the "R" or "A" mark is negative (), then subtract the "R" and "A" value from the measurement6625