Rounded Gear X300 Holster - LUX Universal Holster for Surefire X300X300 Holster LUX Universal Holster for Surefire X300 (Works with the Surefire X300U A or B on Most Firearms.) Our X300 Holster works with almost any firearm as long as the Surefire X300U A or the X300U B fits the stock firearm rail. (*May not work with after market rails or rail adapters.) It does not matter if you have a compact or full size pistol, as long you can mount the X300U to the firearm the LUX will fit. If it has not sunk in yet. No more