I have 2 sockets for Trane centrifical shaft nuts, AN12 and AN22. They a 1/2 drive and are used for tightening shaft nuts with an impact gun. Much better than hammering on the end of a spanner and maybe missing and damaging an impeller. The small socket works on nuts with 3 or 4 dogs. These were built by a machinist and will last many years. Pics if interested.