If I were a betting man, Les, I'd say the orange rubber is just a coincidence due to the spec. I imagine HRC specced the sizes and a 9-ball bearing [which allegedly has a higher speed rating than the 8-ball Koyo], and NTN said "we have just the thing!". I reckon it just happened to have that groove and rubber already, and it was easier to continue manufacturing [or use up the existing stock!] than it was to change them for HRC.

Neither the NX5 or NX6, which obviously produces much more force on the crank than any 250, have that rubber.

This is an NSR500V crank:



Should put your mind at ease!
_________________
Andy.
NSR-WORLD.COM

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