Pistons and rings part number list and compatibility
 

http://pages.sbcglobal.net/jcuadra/p...-ring%20s.xlsx

While looking at compatibility between 94 pistons and 99 rings, Ian made the above spreadsheet from Mazdacomp info.

Now why are there 2 piston part numbers (for a given bore oversize) for 1994, and 1 piston ring p/n, but for the 1999/2000, there is 1 piston and 2 ring sets?