français term (edited): alliance

Since this concerns food processing (see www.agriculture.gouv.fr/spip/IMG/pdf/dgaln20058263.pdf), it is not a matter of stones or fiddly bits catching on things and pulling fingers off, but simply/primarily one of hygiene, so it must not have recesses that could harbour germs.

Apart from anything else, fiddly bits would break off under reasonable force. On the other hand, rings of any kind, including plain bands, ARE dangerous in industrial situations. The classic accident is hand crushing (under a pallet, for example) where the weight traps/crushes the hand but would not in and of itself do any serious damage. Unfortunately, the weight often causes a ring to tilt/turn and move to a horizontal position, thereby sectioning the finger in two places. And even plain bands can snag on machinery and cause fingers to be pulled off.

All machinery can be dangerous, for that matter, jewellery aside. I used to know a girl with long hair who was scalped by a ski-lift ...