Upgrade your full-size XD handgun with the XD OSP (Optical Sight Pistol) Slide Assembly & Kit. These 4″ 9mm kits and assemblies provide original XD owners OSP capabilities as well as the ability to convert certain XD models to a full-size 4″ 9mm configuration. The slide assemblies, featuring included cover plates, are cut to accept OSP optics mounting plates available for a wide range of popular optics.