This is the Nyloc nut for the...
Replacement grip for sculling oar...
Replacement handle for the Model D, E...
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This is the Nyloc nut for the clamping screw on sweep and scull 5 cm Adjustable Grips.
Resources (also available at concept2.com/service):
Scull Handles and Grips Instruction Booklet—see Section II, pp 4–5.