B-RB 3690933 spring what retainer?

Thanks all! Yes the 5/16 valve...seems to be what the numbers recommend for the retainer for this spring.
I will check again on some old heads and stock retainers. I dis try a stock retainer but it seems sloppy and moves around quite a bit as the center of the retainer is small and the spring (933) are a larger diameter than a stock spring. Will take another look and some old heads and pull some retainer to measure.