The Dorma 8812 Offset Slide Arm for RTS88 is used on in the RST31, RST30, RTS29, RST28, RST27, RTS26 and RTS25 packages. This arm is used on Single Acting Doors. The track measures 13" long by 1-3/16" wide by 7/16" thick. This is the arm you probably have if you are using 3/4" offset hinges or 4-1/2" wide butt hinges.
Dorma Part # 8812