The AR-15 Flip-Up MBUS Gen 2 Front Sight by Magpul is a low-profile, polymer backup sight that deploys instantly and is compatible with MIL-STD 1913 Picatinny rails.
It features a spring-loaded ambidextrous release mechanism, requires less than 1" of rail space, and provides the same height over bore as standard A2 iron sights.
The sight is designed for use on a railed forend on the same plane as the receiver rail and is not suitable for railed gas blocks or the MOE handguard.