HP10531 Retaining Ring Replacement for Duplex Spring Handpieces and Adapters

This flat, metal, very tiny but important part is used in each of the following Foredom Duplex Spring type Handpieces or adapters:
H.10D
H.15D
H.18D
H.20D
H.8D
H.8DS-4 1/8 Collet
H.8DS-4 1/8 Collet
H.9D PowerGraver Handpiece
HP775 Adapter
HP776 Adapter

Size is .25″ at widest part or 6.35 mm.