Upgrade your full-size XD handgun with the new XD OSP (Optical Sight Pistol) Slide Assembly and Kit options. Springfield 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.