Survey says! I looked it up in my Machineries' Handbook. Yup. I'll see
if Fastenal has them on Monday.

Ned Simmons wrote:
On Sun, 16 Dec 2007 13:59:03 -0600, Louis Ohland
wrote:
After a bit of puzzlement, I
measured the groove and it's 11.34mm. Shaft is 12mm. Not a whole lot to
play with. I'll get both an 11.50mm and a 7/16th and see which one works.

The nominal size of a retaining ring matches the OD of the shaft, not
the groove diameter. 11.34mm is at the low end of the groove diameter
for a 12mm ring.