Palsonite - Hard surface treatment to make steel surface more resistant against corrosion and wear, and reduces friction. There is no other airsoft manufacturer use this high level technology process on cylinder production, but PDI did it for high end airsfters.

PDI Palsonite Cylinder Set VC (Vacuum System) for Ares AW338 / MS338
Features a high precision laser-cut and cold-hammered cylinder and a tapered cylinder head
Suitable for Bolt Action Airsoft Sniper Rifle
Vacuum Piston Design for flexible airtight adjustment to work with various parts to provide high & stable velocity (Please note that VC Piston needs a little longer time to airproof than HD Piston, velocity might be difference.)
1/100mm tolerance for utmost smoothness and power
Maximum possible power potential on your Ares AW338 / MS338 Airsoft Sniper Rifle
Note that the tolerance level and precision of these parts far surpasses most parts on the market, so they are the choice for professional and serious tuners in Japan

Genuine Products by PDI (JAPAN)

Piston Materials:
The body & The head: Made of Duralmin.
The Ring: Derlin
The End: Stainless Steel