1). The original rear sight leaf AND the rear sight spring must be removed before installing the SKS micro red dot mount. 2). Please make sure that after removing the rear sight spring, you clean the "groove" and remove dirt and dry cosmoline using a sharp object (the tip of a knife will do). 3). Clean all threads, including bolts and threaded holes using soapy water or rubbing alcohol and let dry. BadAce SKS MRD mount Gen 2 supports most Micro Red Dot sights on the market: Shield RMS/SMS footprint - this standard includes: Leupold Delta Point Pro Shield RMS, RMSc, RMSw Shield SMS, SMSc, RMSx Shield SMS 2.0 Sig Sauer Romeo Zero Bushnell RXS-250 MRD sights with the Docter/Noblex footprint - this standard includes: Docter Noblex Sight C, Noblex Sight II & III Vortex Viper, Vortex Venom Burris FastFire 2 & FastFire 3 Leica Tempus ASPH C-more footprint - this standard includes: C-more STS & STS 2 C-more RTS & RTS 2 Vortex Razor Sig Sauer Romeo3 Kahles Helia RD Delta Optical MiniDot HD 24 & HD 26 Trijicon / Holosun footprint - this standard includes: Trijicon RMR, Trijicon SRO Holosun HS407C, Holosun HS507C, Holosun HS508T * * NOT compatible with HS407K and HS507K