TNTrout, Drill stem is a catch all term for oil field pipe. Its usually 2 3/8 or 2 /7/8. Its almost always used pipe of various quality determined by how it was used. A lot of the pipe called drill stem was never used as as true drill stem. More often than not it was used to transport oil or other liquids or to line a well. Some of it is radioactive. A lot of it has a nasty inside coated with suphur. A lot of it from a pump jack will have thin spots where sucker rod rubbed up against it. Its kind of a buyer beware item.
Its a pain to work with a lot of times. I hate it. My pens are made from light weight square tubing and wire panels. Much faster and easier to work with. No coping required. Square tubing with a wire panel is actually very strong as the wire acts like chord members of a truss. A cow may get her front legs on top of it, but since it won't bend, she won't get her back end over. My gates are made to fit schedule 10 handrail pipe. There are always exceptions for real wild cattle and some young bramans can jump like a deer, but I don't deal with those type so my pens work fine. Caustic's pens where you can always keep a gate between you and the cattle is essential at least in your alley ways.