Per what Mal indicated, the AG60 is a partial thread cutter which will cover a pitch range of 48-8 TPI. There are full thread inserts which are spcific to a particular type and pitch thread, really only needed for special threads or if you do a lot of threading with a particular pitch, otherwise go with a partial thread which cuts like 80-90% of the ideal thread. My internal threading tooling originally came with an A60 insert and I often ran into problems with not being able to achieve a deep enough thread cut for the TPI, so the AG60 is preferred unless all you plan to do is finer threads. If you are doing traditional right hand threading you would need an IR type insert, if you flip the bar 180 degrees and cut your thread from the inside out then you need an IL type insert. If you are doing external threads then you would need ER (right hand thread) and possibly EL (left hand thread) inserts. You do not need to buy a ton of inserts, I am still on my original insert after lots of threading and I still have two more cutting tips on the same insert I haven't used.
As far as nomenclature of holders and inserts, and all the nuances, in a way it is like learning a new language and takes time to understand the basics. It took me a long of time to first figure out the types of holders and insert styles that I need. Then I looked at the nomenclature and it started to make sense. There is also two naming standards which is ANSI (imperial) and the ISO (metric) so you can get burned with some of the metric specific tooling that requires metric inserts or proprietary inserts. There is a separate nomenclature for the holders and the inserts they take. In the US ANSI is the predominate nomenclature. The first thing to determine is the size of the holders that fit your lathe holders, so something like a BXA is typically matched to 5/8" tool holders or 3/4" with an oversized holder. The increments for holder sizes is 1/16" so for 5/8" tooling they will be a size 10, 3/4" will be size 12. When you know the tool holder sizes you need you then determine the type/styles of insert you want to use, the rake (positive, neutral, negative) of the insert as it sits in the pocket and the angle of the insert relative to the work (so something like left hand, neutral, right hand, etc.). There are lots of other details, but after awhile it starts to make sense when you start looking at the lathe tooling catalogues. It just takes time, the same holds true for grinding your own cutters.
