6.03mm, the ultimate compromise diameter in Airsoft barrels; just tight enough to make a difference to your power yet just wide enough to not choke on non-premium BBs.
A 6.03mm Diameter is a good compromise when it comes to tightbore inner barrels.
On the one hand, the tighter internal diameter produces a tighter seal against the BB so with less gas leaking around the edges of the pellet that translates to better power regulation between shots as well as squeezing out a little more power which all serves to sure up your weapons accuracy and consistency.
On the other hand, it may not be as tight as 6.01mm version but 01 barrels require premium ammunition due to the more strict tolerances where as 03 can handle normal ammunition perfectly well.
This barrel fits the WE PDW short barreled rfle; installing this barrel into your PDW should go some measure in producing more even results in shot to shot power and show better gas-to-FPS efficiency.