What do you mean by 'internet cable'?
I think that most people (definitely including me ) would think of a conventional Ethernet cable when they hear that term. (Ethernet cables are the ones that connect between a router and a PC if you're not using a wireless connection).
Traditional ethernet cables are copper-wired and are classed into categories (indicated by 'Cat' numbers). Older, and largely redundant, cables might be marked ''Cat 3' or 'Cat 5'. More modern cables might be labelled 'Cat 5e' or 'Cat 6' or higher (although either 5e or 6 is perfectly good enough for almost all home users).
'OM' numbers are only used to label fibre optic cables, with OM1, OM2, OM3 and OM4 being available. I've never encountered a fibre optic ethernet cable being used between a home router and a PC (and search Amazon for 'Ethernet cable' only seems to find copper-wired cables), so I'm mystified as to why you should be looking for an 'OM' number anywhere at all!