In the US the most common standard inch sizes are per SAE AS568C specification (e.g. AS568-214). ISO 3601- 1:2008 contains the most commonly used standard sizes, both inch and metric, worldwide.
The UK also has standards sizes known as BSsizes, typically ranging from BS001 to BS932. Several other size specifications also exist.
Elastomers include Nitrile, Viton, Silicone, Hnbr, and Explosive decompression material, Ptfe, Epdm and Polyurethane.
Shore hardness can be between 40IRHD to 95 IRHD and in some instances coloured rings can be manufactured. Variants on the o ring would be the square section ring and the quad or X ring.