They're called Push-On External Retaining Rings.
And yes they need to be CAREFULLY cut-off with dykes/side-cutters to get them off without damaging the Plastic Pins they're mounted on.

B/W used the same thing their WPC-95 Speaker Panels - Terry @ Pinball Life has these - fits 1/4" Posts:
https://www.pinballlife.com/14-push-nut.html

Here's a link to where I've gottem them in bulk and most good Automotive stores should keep a few sizes in stock:
https://www.mcmaster.com/push-nuts/push-on-external-retaining-rings-6/