If you are talking about these items
They are superb. [Make sure
to order the proper modified case case(s) when
you order the (long/skinny thing) OAL guage.]
As far as the comparator inserts go, there is one (in the set) for every caliber. They are
to engage the bullet at bore/lands diameter so as to get a true reading of
the proper (comparator) length of the cartridge relative to those lands. Every different
bullet design will therefore have its own different measurement.