| Diagram | Fig. 4 — CYLINDER BLOCK AND HEAD, 6T AND TR6 · ref 4 |
| Subsystem | engine top |
| Listed in parts books | 1960–1965, 1967–1968 |
Outer cylinder base nut
Outer cylinder base nut used to secure the cylinder block to the crankcase on Triumph 650 twin engines.
P0172A is the outer cylinder base nut, a fastener that shows up repeatedly in the cylinder block and head figures for the 6T, TR6, TR6R, TR6C, and T120/T120R engines. It's one of the nuts that secures the cylinder block down onto the crankcase studs, working alongside the other base nuts to keep the barrel seated correctly.
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This part number turns up across a wide range of catalog sections beyond just the cylinder block figures, including engine fittings, footrests, frame, and suspension listings, which just reflects how parts books group common small hardware across sections rather than telling you anything new about the part itself. The core job stays the same: it's cylinder base hardware.
We don't have more detail on this one in terms of thread size or material, so if you're ordering a full set of base nuts, give us a call and we'll confirm what you need before it ships.
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