If you need an optic for your Glock 43X, I’m here to help. The Modular Optic System, or MOS, version of the G43X has a factory cut slide that accepts only micro-footprint sized optics using the RMSc-type base. Not every red dot sight (RDS) will fit.
Initially popularized by the Smith & Wesson Shield series, the RMSc footprint is now used for a range of guns including the SIG SAUER P365 series and the Springfield Armory Hellcat optics. The sights are more compact than normal pistol red dot sights and are necessary for slim guns like the G43X.