The  RM45 is for M300 or M600 Series and the RM45L for M620 Series.

The RM45 mount securely attaches any thumbscrew-clamp-equipped Scout Light to a MIL-STD-1913 rail and puts the light in the off-set position between rails, decreasing overall weapon profile and limiting snag factor. The RM45L offers the same capabilities, but was built for M620 Scout Light models that feature Swing-Lever™ clamps.