Titanium LC with some modifications:

The window retaining lip in the stock head was opened up to an ID of .785" to allow the McR-20 a full passage of reflected light. A 1 mm x 20 mm O-ring seats between the window and bezel lip. A custom heat sink was machined with a height on the top of the LED moat such that it compresses the a compression sleeve coupling between the reflector and the heat sink against the window and seal. The heat sink has a slug on the bottom that centers it on the Ti converter module. A #2x56 fastener clamps the heat sink against the face of the converter module as well as provides for a common ground path with a coiled and tined lead wire under it. The Lux III (UX1J) is bonded to the heat sink with Arctic Silver epoxy and the light is capable of simple candle mode with removal of any of the heads.

The 20 mm reflector is captive in the head by an O-ring on the compression sleeve which has an interference fit in the bore of the head. The 20 mm, 27 mm and 38 mm heads all have captive reflectors and cay be swapped around on the light at will. All three reflectors are in compression with the heat sink and they provide additional thermally conductive mass for immediate relief of the LED. In any long run times, the 27 mm and 38 mm heads of aluminium will also provide thermal relief.