The Independent Drop-In Rear Sight (IDRS) from Parker Mountain Machine is the most low-profile and least obtrusive rear iron sight on the market. Small enough to be there when you need it, and barely noticeable when you don't, the IDRS mounts directly to your Trijicon SRO. This rear sight requires the following front sight heights: Direct Milled Slides at industry standard .125 deep requires a .350 tall front sight. GLOCK MOS with industry standard .100 thick optic plates require a .390 tall front sight. *PLEASE DO NOT CONTACT PMM FOR SIGHT HEIGHT INFO. IF YOU HAVE QUESTIONS ABOUT PROPER HEIGHTS, PLEASE EMAIL INFO@CHPWS.COM