Sta-Kon RG727U NYL INS LRG RNG TRM 90 DEG No2 RED

The RG727U is sized for 2 AWG conductor. It is a large nylon insulated ring terminal, so it is meant for heavy single-conductor runs like battery, feeder, or panel grounding leads rather than control wiring. If your conductor is 4 AWG or 1/0, this is the wrong barrel size and a crimp on it will not hold.

The RG727U is a flag-style terminal: the ring sits at a right angle to the barrel, so the wire runs parallel to the mounting surface instead of straight into the stud. That is what you want in a tight panel, on a busbar face, or at a battery post where a straight terminal would force a hard bend in a stiff 2 AWG conductor. If you have room to come at the stud head-on, a straight ring terminal is the simpler part.

Yes. At 2 AWG this is a heavy barrel, well past what a hand-squeeze insulated terminal tool will close. You need a large-gauge crimper - a hydraulic or ratcheting lug crimper with dies that cover 2 AWG. Crimping it with an undersized tool leaves a loose connection that heats up under load.

The red on the RG727U is the nylon insulation color. On Sta-Kon large ring terminals the color is a size indicator used on the shop floor to tell barrels apart at a glance; here red corresponds to the 2 AWG barrel. Do not read it against the small-terminal color scale (red/blue/yellow for 22-10 AWG) - this is a large terminal and the color code is not the same family.

Nylon is the body material on the RG727U. Compared with vinyl insulation, nylon resists abrasion and cut-through better and holds up when terminals are packed tight against each other or pulled through a wireway, which is why it is the usual choice on larger gauges where the conductor is stiff and the installer is forcing the lug into position. For a fully sealed connection you would still need heat-shrink or adhesive-lined tubing over it; the nylon sleeve is mechanical insulation, not a moisture seal.