This casement window operator is a left handed aluminum square body type . It has a 9 in. steel arm with a round disc on the tip (some older styles had a small wheel instead of a disc). The disc slides in the Prime-Line part H 3529 casement track located on the bottom of the casement window. It is worm gear driven by a 3/8 inch crank spindle. The matching crank handle that fits onto the crank spindle and installation screws are included. Mounting holes available are 3-7/8 & 4-3/4 inches apart.