Sta-Kon RE10711U NYLINSUL RNG TERM 90 DEG No6AN BLUE

Yes. The RE10711U is specified for 6AN wire size, so it is the right barrel for that conductor. Terminals are not interchangeable across sizes, a conductor that's too small for the barrel won't hold crimp tension and one that's too large won't seat fully, so confirm the wire you're landing matches before you crimp.

No. A ring terminal is a closed barrel, the stud or screw has to come all the way out so the ring can be slipped over it. If the screw stays captive in the block, you need a spade or fork style terminal instead, which slides in from the side. The tradeoff is that the closed ring can't vibrate loose off the stud, which is why ring terminals are preferred on motors, bus bars, and anything that sees movement.

It's a nylon insulated ring terminal with a 90 degree bend in the tongue, so the ring sits perpendicular to the wire run. That lets you land a wire on a stud or screw terminal where the conductor has to approach from the side, instead of forcing a bend in the wire itself. Insulation is nylon, which holds its shape and resists cracking when the barrel is crimped.

Pick the 90 degree version, like the RE10711U, when the stud or screw you're landing on faces a different direction than the wire approach, inside a tight panel, on a bus bar at the back of an enclosure, or on a motor terminal block where a straight terminal would force a sharp bend in the conductor. A straight ring terminal is the simpler choice any time the wire can run in line with the stud. Both land on a stud and both need the stud to pass through the ring, so the choice is purely about geometry in the enclosure.

The RE10711U is a blue terminal. On nylon and vinyl insulated crimp terminals, insulation color is the industry wire-range code, and blue is the mid range between the smaller red barrels and the larger yellow ones. Use the color to sort terminals on the truck, but match the barrel to the actual conductor gauge you're terminating rather than picking by color alone.