Mounting rings made of stainless (surgical) steel 304, diameter 4mm, cross-section 0.5mm, internal diameter 3mm.
This steel is not a precious metal, but it is an order of magnitude higher in all respects than other jewelry alloys (brass and zinc alloy). This material has high anti-corrosion properties, does not cause allergies, is resistant to human sweat, sea water and the sun - which will ensure a long life for your product