It has come to my attention that a few pointers would be helpful so I am posting this to help clear some confusion.
1.) To change modes, turn the light on then depress the switch minimally and let it go. It should switch between the modes with a bit of practice.
These do have a mode memory so whatever mode you turned it off in is the mode it will start in next time.
2.) The rail mount fits over the pressure switch, not the light body itself.
If you want to slide the light into the rail mount a brake hone makes short work of it.
3.) when installing the aspheric lens, a pair of needle-nose or split ring pliers will help unscrew the bezel. Remove the glass and the o-ring behind it. Then the Aspheric fits better and works better.
Leaving the o-ring in will not allow for a full seating of the bezel. Again milling the head or the bezel can allow for use of the aspheric with the o-ring if a waterproof seal is required.
4.) Most surefire 6P accessories will fit but are more expensive than their contemporaries.
5.) No other battery will work in these lights. They are optimized for the current and voltage provided by these cells.
6V heads can be made if you need to use CR123 primary cells but be warned they dont last very long (like 25 minutes a pair on high) and they are expensive ($2-5 each).
6.) If you need to lube the threads on the head or tail of the light. Don't use petroleum products as they may damage the o-rings and thus the waterproofing.
Superlube from Ace Hardware or Plumbers Silicone grease ($3 and change) from Lowes/Home Depot are both excellent choices.