Marvin Classic Old Style Case-Master Casement Windows, Marvin Clad and Wood Old Models - Dimension "B" Lengths of Short Arms May Vary from lengths of  4 7/16", 2 7/8"  and 3 3/4" CASEMASTER, AWNING, FRENCH CASEMASTER UNITS - Casement Operator Replacement Parts - Old Obsolete Parts RF-15, 20810, 30744,  20811, 30841, 30842, 30741, 30742, 31538, 31539, 30472, 30470, P234DC P233DC and others; Casement Window Crank Operator Mechanisms For Old Model Marvin Casement and Awning Windows. 

Specify Handing In The Comment Section At Checkout - left handing or right handing ( SEE PICTURES )   DETERMINE AS FOLLOWS: looking at the window from the inside - if the "lock" or "lock handle" is on the left, a left handed operator is needed. If the lock or lock handle is on the right, a right handed operator is needed.