[1] Frangible nuts secured the solid rocket boosters (SRB) of the Space Shuttle, which were bolted to the mobile launcher platform (MLP) until liftoff.
The broken nut and any fragments from detonation were captured by energy absorption material, such as metal foam, enclosed in a blast container to prevent damage to the shuttle.
At launch, two pyrotechnic, or explosive, devices "break" a frangible nut into two halves, allowing the stud, which is under high tension, to eject into the hold-down post system and release the space shuttle from the MLP.
At liftoff, a stud not ejected prior to the first space shuttle movement, which occurs approximately 200—250 milliseconds after ignition, becomes bound and/or pinched and results in a hang-up.
At liftoff, each detonator receives a "fire" signal, which in turn initiates the booster cartridges, causing the frangible nut to fracture.