Height measurements are from top of base to center of ring:
Super Low, .550" (13.9mm).
Low, .650" (16.5mm).
Medium, .770' (19.55mm).
High, .900' (22.86mm).
Super High, 1"(25.4mm).
Extension Ring Set (Extension) contains one standard ring, and one front extension ring that offsets ring spacing .650" (16.5mm).