The Modlite light 18350 Body is designed as a direct replacement body for Surefire® Scout Light M600DF weapon lights and the KE2-DF head. This is the only Surefire light head that it is compatible with. It is approximately 1.25 inches shorter and about 1.5 oz. lighter than a M600DF body with battery. This allows for additional rail space especially on SBR and pistol builds. The Modlite 18350 Light Body is compatible with Surefire® z68, Modlite TCC tailcaps along with Surefire UE and DS00 tail caps. It will also fit in any aftermarket Scout mount, as it retains the mounting holes and square lug interface on the underside of the light body. This light body accepts 18350 cells only. Lithium CR123 cells are not supported and if used will cause the cells to heat up and possibly explode or catch fire. Modlite recommends the KeepPower high drain 18350 1200mAh cells. Runtime is about 35-40 minutes with these cells. The Modlite light 18650 Body is designed as a direct replacement body for Surefire® Scout Light M600DF weapon lights and KE2-DF heads. It will also fit all Modlite light heads. The Modlite 18650 Light Body is compatible with Surefire® z68, Modlite TCC tailcaps along with Surefire UE and DS00 tail caps. It will also fit in any aftermarket Scout mount, as it retains the mounting holes and square lug interface on the underside of the light body. Modlite recommends and sells the Arisaka Defense mounts. This light body accepts 18650 cells only. Lithium CR123 cells are not supported and if used will cause the cells to heat up and possibly explode or catch fire. Modlite recommends the KeepPower high drain 3500mAh cells. Runtime is about 75-80 minutes with these cells. The Modlite 18650 light body is NOT compatible with the Surefire older Scout light heads.