| Also known as | S578 |
| Diagram | Fig. 20 — TELESCOPIC FRONT FORK · ref 9 |
| Subsystem | forks front |
| Listed in parts books | 1967–1974, 1976–1980, 1983, 1985 |
Grub screw - twinseat lock
A shear-head grub screw that locks a Triumph twinseat or steering lock in place once the head is snapped off.
This is a small grub screw used to secure the twinseat lock (also seen in the parts book tied in with the fork lock hardware). It's a shear-style set screw: you thread it in against the lock body until it seats, then the head snaps off, leaving the shank flush and tamper-resistant so nobody can back the lock out with a screwdriver.
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The part shows up across a long run of catalog entries, from telescopic front fork figures through gas tank and twinseat listings, so it served double duty on both seat locks and fork-mounted steering locks depending on the model and year. The legacy alias S578 is the same physical piece under the old numbering.
It's cheap to keep a spare of since it's meant to be sacrificed once installed - if you ever need to service the lock behind it, you'll be drilling out the stub of this screw to get in.
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