3M 7000133421 3M™ Scotchlok™ Ring Vinyl Insulated, 50/bottle, MV10-38R/SX, standard-style ring tongue fits around the stud, 500/Case

The MV10-38R/SX ring terminal is sized for 12 to 10 AWG stranded copper (3.31 to 5.26 mm2). That is the yellow color code, so if you are working 16-14 AWG or 22-18 AWG on the same panel you need the blue or red barrel instead, not this one.

Both. The Scotchlok vinyl insulated ring is rated 600V for building wire and 1000V for signs, fixtures and luminaires. It is UL Listed, CSA Certified and RoHS 2011/65/EU compliant, which covers most inspected commercial and institutional work.

Operating range is -40 to 221 degrees F (-40 to 105 degrees C), so a rooftop unit disconnect in a Minnesota winter and a boiler room ceiling are both inside the envelope. The barrel is electrolytic copper with tin plating for corrosion resistance, which is what you want in damp or salt-air locations.

Use the ring where the connection must not back off. The ring tongue is a closed standard-style loop that has to go fully around the stud, so the nut has to be removed to land or remove the wire, and vibration cannot walk the conductor off. A fork or spade slides in under a loosened screw, which is faster for service work on a dense terminal strip but can shake loose. For motor terminations, grounding studs, and anything that vibrates, the ring is the right call.

These are crimp-only, mechanical terminations. The vinyl sleeve is not heat shrink, so there is no torch or heat gun step. Use a standard insulated-terminal crimper set for the 12-10 AWG (yellow) die position. The sleeve mouth is funnel shaped so stranded conductor feeds in without splaying strands outside the barrel, which is the usual cause of a failed pull test.

Country of origin is the United States, which is worth noting on government and institutional jobs that carry domestic sourcing language in the spec.