This is a standard sized case race for the left hand side case for Bigtwin Flatheads (1940-48). This race will also fit Bigtwin Flatheads (1937-39) after case modifications have been made. We recommend that the 1937-39 models use this later race case to insure that cases can be line reamed. We offer this modification as a service.(Call for details) We also carry case races for the overhead valve motors - (please call for information and prices). Made in the USA