I have a Price Pfister shower head that evidently does not have a standard thread size because I bought a standard shower head that will not install. Did Price Pfister use a different diameter about 12-15 years ago? Do stores like Home Depot or Lowe's sell an adaptor to allow me to drop down to the smaller size (standard size)? Thanks!

The standard thread size for a drop earred ell, shower arm and head is 1/2" IPS. This hasn't changed over the years. Regarfs, tom

If the weird thread is on the end next to the shower head and not back in the wall, the easiest thing may be to unscrew the arm going back into the wall. Likely that end does have the standard 1/2'' pipe thread. Then you should be able to buy a new arm with the right threads.

If you have trouble unscrewing the arm, post back before you twist it off. There are solutions to twisted off pipes, but it is easier to loosen them up instead.