Wikipedia's Frangible nut begins:

Not to be confused with Explosive bolt.

The frangible nut is a component used in many industries, but most commonly by NASA[citation needed], to sever mechanical connections. It is, by definition, an explosively-splittable nut. The bolt remains intact while the nut itself is split into two or more parts.[1]

Space Shuttle

Frangible nuts secured the solid rocket boosters (SRB) of the Space Shuttle, which were bolted to the mobile launcher platform (MLP) until liftoff. On the Shuttle, they were separated using a NASA standard detonator (NSD). The space shuttle used two NSDs for the frangible nut atop each of the four 28-inch-long (71 cm), 3.5-inch-diameter (8.9 cm) bolts holding each SRB to the MLP. Once detonation occurred, the shuttle lifted free of the MLP. The broken nut and any fragments from detonation was captured by energy absorption material, such as metal foam, to prevent damage to the shuttle. In case of NSD failure, or incomplete clearance of the nut from the bolt, the SRB had ample thrust to break the bolt itself and launch unhindered.

and "frangible" appears in at least 15 posts here.


  1. What was the first instance of frangible nuts in space?
  2. Which space-nuts were first successfully "franged"? (could be the same ones)
  3. What's the origin of the exact term "frangible nut"? Was it first coined in the context of spaceflight, or was nut-self-franging already a thing?
  • $\begingroup$ Would a “pyrotechnics” tag be useful? $\endgroup$
    – uhoh
    Mar 21, 2021 at 1:43
  • 1
    $\begingroup$ As a slight clarification, or perhaps elaboration to "Once detonation occurred, the shuttle lifted free of the MLP", it's not as if the bolts were holding down the Shuttle and preventing it from launching. In fact they probably could not have. The bolts held the Shuttle in place during transport, and while sitting on the pad including windy conditions. At ignition they held the stack steady on the pad as the SSME's ramped up to liftoff thrust, and swayed back and forth (twang). At T-0 the SRB ignition and nut detonation commands were issued essentially simultaneously, 8 milliseconds apart. $\endgroup$ Nov 16, 2023 at 12:36
  • $\begingroup$ @StevePemberton just fyi, I've added a bounty... $\endgroup$
    – uhoh
    Nov 20, 2023 at 2:47
  • $\begingroup$ Oxford dictionary: late Middle English: from Old French, or from medieval Latin frangibilis, from Latin frangere ‘to break’. $\endgroup$
    – Woody
    Nov 22, 2023 at 15:56


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