GR600 Arm
GR600 Swing Gate Opener (Arm Only as per the photo)
If you are not sure of which model you have you can measure the length of the grey barrel tube. There are 2 lengths GR400 = 490 mm and the GR600 = 690 mm
They also come in a left = S and a right = D. On the top of the housing is a letter stamped into the casting.