I've used the split ring protector for saucer holes shown at the link below from Mantis Amusements. I have 3 on my WCS94, 1 on my HS2, 1 on TOTAN, and 1 on my TAF skill shot saucer (customized to fit). I usually secure them with a tiny finishing nail thru a hole I pre-drill in the split ring protector. Otherwise they tend to work themselves out of the saucer hole.
https://mantispinball.com/product/tales-of-the-arabian-nights-protector-set/