found a site which covers some coating abbreviations, quote Phos (P & O) Phosphate and Oil Coating (typically Zinc Phosphate and Oil)
Pozi Drive Special cross recess (registered trademark of Camcar Textron)
PPAP Production Part Approval Process
psi Pounds per square inch
PZ Pozi-Drive style of cross recess
Zn Zinc, usually referencing zinc plating (assumed to be zinc with clear chromate)
Zn/C (ZC) Zinc Plating with Clear Chromate topcoat
Zn Phos Zinc Phosphate and Oil (same as Phos and Oil)
Zn/Wax Zinc Plating with a topcoat of wax
Zn/Y (ZY) Zinc Plating with Yellow Chromate topcoat
http://www.earnestmachine.com/OnlineCatalog_TechnicalLibrary...