What it is and what it fits
The 1-330518-1 is a Plasti-Grip ring terminal from TE Connectivity AMP Connectors, designed for 10-12 AWG wire and a #10 stud size. It uses a tin-plated copper contact with a serrated crimp barrel, insulated in yellow PVC, and is rated for free-hanging (in-line) mounting.
What the insulation diameter means for the wire you're running
The insulation grip accepts wire insulation diameters from 0.200" to 0.300" (5.08 mm to 7.62 mm) — the range covers the jacket of most 10-12 AWG stranded building wire and automotive primary wire. Overall length is 1.111" (28.22 mm); the outer width across the barrel is 0.312" (7.92 mm).
How the Plasti-Grip compares to a non-insulated ring
Unlike the non-insulated Solistrand rings (1377172-7, 133521-1, 1377172-9) which use a brazed-seam barrel and thinner 0.031" (0.79 mm) stock, the Plasti-Grip 1-330518-1 carries a thicker 0.039" (0.99 mm) copper body and a full PVC insulation sleeve — the insulation provides strain relief at the wire entry and prevents accidental shorts against a grounded panel.