Originally Posted by
Badger6
You cannot install the non-drive side (left) crank arm incorrectly. The splines are keyed, meaning they are not equally sized and spaced, to ensure that the left arm can only be installed onto the spindle at 180° from the drive-side crank arm.
Well actually... You can totally install it at 0 degrees if you like, and folks who pedal with their arms do. It'd be nice if Shimano would put another hole for the check pin for these peeps...