Yes, that's a magnet ring for Avocet (I think it worked with model 20, 30 and 40) bike computers from the 80's.
They actually came with different mounting prong locations to work with either 36 or 32 hole front hubs.
A time. pickup sensor for it is mounted just above the fork dropout with a small zip tie. A very clean design for the time.
The Avocet model 20 I bought for my Peugeot PSV back in 1984, is still on the bike and still works!
Last edited by Chombi1; 09-26-21 at 12:17 AM.