Sig Sauer Romeo-RS in the Pro footprint - the larger mounting pattern designed for duty and full-size pistols. Same enclosed-emitter design as the Compact variant; the wider footprint mates to RMR-cut and DPP-cut full-size slides via the Pro adapter system. 3 MOA dot for precision-balanced duty/carry use. Specs: Reticle: 3 MOA red dot Housing: aluminum, matte black, fully sealed enclosed emitter Illumination: motion-activated, multi-brightness Battery: top-loading Footprint: Romeo-RS Pro - fits full-size duty/competition optic-ready slides Pro footprint use case: Glock 17/19/45/47 MOS, Sig P320 XSeries, P229 RX, Beretta APX, S&W M&P 2.0 OR. If your pistol is a full-size optic-ready model and not a slim subcompact, you want the Pro footprint.