Chamberlain C870C Owner's Manual page 9

Outer Lock
Nut Washer
To Tighten Outer Nut
To Tighten
Inner Nut
Chain
Base of Rail
Mid length of Rail
Trolley
Threaded
Shaft
Inner Nut
1/4" (6 mm)
HARDWARE
Hex Screw #8x3/8"
(Packed with the sprocket cover)
Hex Screw
Sprocket Cover