Originally Posted by
Bikedued
I think it's a cap over the nub. I have seen that before on some Dia Compes, though it's been a while. I am fairly certain they weren't resissues at any rate.,,,,BD
I can confirm that it is a small cap over the nub. When I took apart my brakes for cleaning I found that oddly enough only my front caliper had the little plastic cap over the nub.
This thread has been very useful as I have encountered this same issue with using narrow rims on my Raleigh.