Barry,
The guys have given you a lot of good information, at the risk of covering some ground again, here are some things I can contribute.
Generally speaking rail is 39’ long. The next lower standard length is 33’, which is what you get when you crop the ends of a 39’ rail. When improperly maintained, or from age, the rail ends get bent down and the only way to fix that is crop it. Of course, this adds more joints, which means more maintenance. It’s a vicious cycle. There is a machine out there called a rail straightener which sounds like a good idea. Unfortunately, after being straightened with one of these machines (And even while straightening), a fairly large percentage break.
After the 33’ length you get the “shorts”, which are anything needed to fill a gap.
FB or Flat Bottom rail must be a UK term, it’s not a term used in the US.
Rail is designated by the weight per yard, 90, 100, 130, etc. There are also letters in that rail designation, PRR, PS, LV, RE, ASCE, etc. Many of these are the railroad that came up with this rail section, PRR, LV and RDG are pretty self-explanatory. PS is Pennsylvania Standard, I can’t remember what RE means, but there are enough rail sections out there to give you a headache. Plus, they have many different spacings for the drillings on the ends, so the bars and rails have to match.
There are also numerous types and sizes of tie plates, rail anchors, and even track bolts (Nuts and washers too) that match the various rail sections. And that’s not even getting into the plates and other jewelry that goes with welded rail on wood or concrete ties.
The only joint bars with inside/outside that I’m familiar with are Compromise (Comp) Joint bars. These are exactly what they sound like, they compromise the joints between different rail sections. They come in left and right hand versions due to the head of the rail being a different width and the need to keep the gage the same on the “gage” side. Railroads don’t ca