The insert in solid carbide and the outside is jacketed in steel, a solid carbide ring would be heavy and subject to damage on the outside due to carbide being hard and brittle.
Rings below 1.510" are manufactured without a flanged outer diameter. The designs for cylindrical ring gages are described in ASME standard B47.1
All cylindrical Rings are manufactured to ASME/ANSI B47.1 AGD standard and ASME/ANSI B89.1.6. All rings regardless of size are lapped to size and polished. Sizes available up to 28".