Originally Posted By: mjoekingz28
Ok, here is what I have so far
TG is for tough guard
HM is for high mileage
XG is for extended guard
What in the world is PH?
What? You guys throwing softballs now? This one is easy. The PH designations go back to ww2 era. In fact, PHXX is the most widely used oil filter numbering system in the world copied by many other filter makers. It pre-dates the "Guards" by a very long time and was so entrenched that even our marketing group wouldnt change it.