The Dorma 8831 Top Arm for RTS88 is for use on Single and Double Acting doors. This arm is known as a side load arm, and usually has a notch in the door at the top to access the arm fastening block. This piece measures 10-1/2" long by 1-3/8" wide at the widest part, and is 1/2" thick. This is the standard arm in the RST01 and RST02 Packages.
Dorma Part # 8831