| Also known as | S1-51, S151C |
| Diagram | Fig. 9 — GEARBOX OUTER COVER · ref 35 |
| Listed in parts books | 1960–1970 |
5/16X26 NUT CHROME
A chrome 5/16-26 TPI bar-cut nut used on various British motorcycle fasteners, including crankcase studs.
This is a 5/16-26 nut, chrome finish, part number 21-0151C. It's a bar-cut nut on the CEI 5/16-inch, 26 TPI thread standard, one of the common small fasteners you'll run across on British twins of this era, often turning up on crankcase studs and bolts. Because it's bar-cut, it wants a washer under the base rather than sitting flush against the case.
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The part carries older catalog forms too, S1-51 and S151C, so if your parts book lists one of those numbers you're looking at the same nut. Given how many spots on the engine and chassis use this thread size, it's worth checking exactly which stud or bolt you're replacing it on before you order, since fit is more about the thread matching than the nut itself being unique to one location.
We don't have more detail on this one beyond the description and thread spec, so if you're unsure where it goes on your bike, give us a call and we'll help sort it out.
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