Sta-Kon C485 NON-INS RECT RING TERM, 12-10, No4

It's a No. 4 ring, so it lands on a #4 screw or stud. On smaller terminal blocks and device screws that's the common size, but confirm the stud on your breaker lug or bus before ordering, since a #4 tongue will not slip over a #10 or 1/4-20 stud.

It carries UL file E9809 plus CSA 4503 and CSA 7222, so it satisfies the listed-connector requirement on both US and Canadian inspected work.

Bare metal. It's a non-insulated rectangular ring terminal in copper with a metallic finish, so if the connection needs to be covered you add heat shrink or a separate nylon sleeve after crimping. Where inspectors want insulated terminations, choose an insulated ring terminal in the same 12-10 AWG range instead.

The rectangular tongue gives you a flat, squared body that seats against a bus bar or block face without rotating, while still being a closed ring, so the wire can't come off the stud if the screw backs out. A fork or spade is quicker to slip on and off but will release under a loose screw. For a connection you don't plan to service often, the closed ring is the right call.

No. The barrel is copper, which makes it a copper-conductor terminal. Aluminum wire needs a connector marked AL or AL/CU with the proper inhibitor compound; putting bare copper on aluminum invites galvanic corrosion at the joint.

It's a non-insulated barrel in the 12-10 AWG range, so it crimps with the non-insulated (uninsulated) nest of a standard terminal crimper, not the colored insulated dies. Using an insulated-die crimper on a bare barrel gives you an under-formed crimp.

Yes, country of origin is the United States. That matters on government, school district, and federally funded MRO work where domestic sourcing is written into the purchase order.