Thomas & Betts Steel Conduit Bushing

Three sizes: 1/2 inch (part 122), 1 inch (part 124), and 1-1/4 inch (part 125-TB). Order by the trade size of the conduit or fitting thread you're bushing, not by the conductor size.

Yes. The 125-TB is sized for 1-1/4 inch trade size, and conduit bushings use standard tapered conduit thread, so it threads onto 1-1/4 inch rigid or IMC ends and matching 1-1/4 inch hubs and fittings. A 1 inch or 1/2 inch conduit needs the 124 or 122 instead.

Steel. If your spec or inspector calls for an insulated bushing to protect conductors at the raceway end, a steel bushing on its own won't satisfy that, you'd want a plastic insulating bushing or an insulated-throat metal bushing instead.

It threads onto the exposed end of a conduit or nipple inside a box or enclosure to cover the raw thread and give conductors a rounded bearing surface as they turn out of the raceway. Electricians also use them to lock a nipple or to take up the thread on a chase nipple run through sheet metal. These are steel, so the thread face is the wearing surface, not a plastic throat.