The H 3508 casement window operator is a right hand aluminum teardrop 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 H 3529 casement track located on the bottom of the casement window. It is worm gear driven by a 5/16 in crank spindle. The matching crank handle that fits onto the crank spindle and installation screws are included. Mounting holes available are 3-7/8 and 4-3/4 in apart.