Is there any mekor to the minhag of kashering rings?
The potential mekor to it, is that they use the rings when they work with hot chometz food, such as hot challos when they are taken out of the oven and they will work with hot pesach food when the ring is on their fingers. However even so, there are others that question this chumra, and there are different opinions as what should be done. Some say that if they are cleaned very well it is sufficient. Others say that pouring hot water over them is sufficient. If you are afraid that it will cause the ring to break, then just clean them well and the ring can be soaked for a few minutes in some sort of detergent, such as ammonia to make sure that anything left on it is no longer edible. Others say that after they are cleaned that they shouldn’t be used for 24 hrs. before Pesach.
Madreichei Kashrus of the Eida Hachareidis, Sefer Hagolas Keilim 13ftnt 115, Ohel Yackov pg. 47 in the name of R’ M. Bransdorfer zt”l that if there is any fear of it breaking that pouring hot water over it is sufficient, Halichos Shlomo NIssan pg. 52 ftnt. 51, The Kosher Kitchen pg.404.