This is also what I would have understood of anneau de rappel, out of context.Are you sure it's jewellery? I'd normally expect that to refer to an abseil/rappel ring.
As read in the description of this bracelet (I have yet to learn how to insert a small image like Hildy did )Longueur bracelet : 18cm avec anneau d'ajustement à 16cm.
Longueur collier : 45cm avec anneau d'ajustement à 42cm.
Chaîne en or blanc. Longueur 42 cm, anneau d'ajustement à 40 cm.
I also read adjustment ring (rather than adjustable), but sizing ring sounds right to me.17.50 cm length with sizing rings at 14.50 cm and at 16 cm.
The second example is copied from the website of a jewelry store located in Pewsey, Wiltshire, U.K.adjustable silver 925 charm bracelet
length : 17 cm with adjustment ring at 16 cm
handmade in Paris (with love)
Three adjustment rings are are available to fasten with t-bar so that the bracelet can be worn at the shortest length of 170 mm and longest 210 mm.