Internal diameter is 6.01mm.
Made of Stainless steel.We could product 01-inner barrel by using new technology of 05-inner barrel.
The tolerance is ±0.002mm
05 inner barrels are producted by using the Cold hammering(This tolerance is the highest quality in our industry).
But it's impossible to product the internal diameter 6.01mm.We needed more accuracy.
So we reaquired more precise scale.
01 barrel is pro model,not 05 barrel.If they have extreme precision diameter,they may affect from using which BB,situation,maintenance & other facters. Please be careful.