PDI 6.1+mm precision barrels are the more wallet friendly barrels from PDI. They are made of carbon steel and then given a chemical coating for enhanced durability. The bore tolerance is +-0.007mm whereas their SUS304 barrels are made to +-0.002mm, but still provide a significant improvement over stock barrels and many other wallet friendly upgrade barrels.
For AEG/ Tokyo Marui TM AEG.
Inner Diameter: 6.1+mm
Made of carbon steel with a chemical coating