These are also called “Bearing Preload Collars” and are part of the non-drive side/left crank arm assembly on our M/A/R/G 30 cranks.  The collar threads onto the crank arm and adjusts the bearing preload of the bottom bracket.  Make sure the collar is threaded all the way onto the crank arm before installing the arm onto the spindle, otherwise you may damage your bottom bracket bearings and/or crack the collar.

 Tools

• 1.5mm hex key

 Bottom Bracket Bearing Adjustment

• Adjust collar to remove side-to-side play, then back off 1/8th of a turn

Pinch Bolt Torque

• ¼ turn past snug (more may crack the collar)