Compatible with HK MP5, and clones such as Century AP5/K, Zenith ZF5/K and Military Arms Corporation MAC 5/K. This product is not compatible with any MP5 .22LR firearms. This rail is designed to fit 9mm receivers; there may be fitment issues with the 40cal/10mm receivers. Gen 2 version includes a longer 1913 rail, better clearance around the charging handle, and lightning cuts for aesthetic upgrade. Easy no gunsmith install, all tools included Allows the user to mount an optic and a light or laser while retaining the factory handguard Forward M-LOK slot allows mounting of additional accessories Constructed of Hard Coat Anodized 6061 Aluminum for a lifetime of service Made in the USA 922R Compliant Lifetime Warranty