| Listed in parts books | Not catalogued by year yet |
CYL BASE NUT 12PT 3/8X24
12-point cylinder base nut, 3/8x24, for securing the barrels to the crankcase.
This is the 21-0692A cylinder base nut, a 12-point nut cut 3/8x24. Twelve-point nuts like this one are used where a socket or spanner needs a positive grip in tight quarters, and cylinder base fasteners are exactly that kind of spot on a Triumph twin - down where the barrels meet the crankcase, working space is limited and the standard hex nut isn't always the easiest thing to get a wrench on.
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The alias 9998-862 is another number this same nut has carried in the parts books, so if you're cross-checking against an older listing and see that number instead, you're looking at the same part.
We don't have much more history on this one beyond what's in the description. If you're rebuilding a set of base nuts, it's worth having a few extras on hand since they don't wear out gracefully once the threads or the points get worn down from repeated use.
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