I am doing and inventory of our thread gages and have come across several odd gages. They have a -2 on the end of the size. For example: 1 1/8-12NF-2. It's on the GO and the NO-GO ring. The pitch diameter is slightly larger on these -2 ring gages than on the standard gages. Couldn't find any info in the Machinery Handbook. Can anyone explain these?