The Casement Operator 9" Arm has a die cast housing with steel arm. This mechanism was popular 30 years ago, and was used on steel and aluminum framed windows. The hole spacing of the window operator housing is 4-3/4" on the outside screws and 3-7/8" on the inside two screws. The arm is 9" from the roller to the center of the window operator housing. This operator uses a 5/16" spline operator, part #Ro169516.