The milled receiver MAK-91 has a.684' diameter barrel and the NHM-91 has a.668 diameter barrel. The Maddi post bans have.580' diameter barrels and Romanian's are.584'.
All AK's have barrels that are 4 different diameters in different places. The chamber is the largest diameter then steps down at the rear sight block, next the gas block, and finally the smallest diameter is at the front sight. All Poly Tech AKs have an oval 386 stamped on the receiver. All the milled receiver Chinese rifles have 386 in a oval. The post ban models MAK-90,MAK-91,AK Hunter and Poly Tech Legend pre bans have the 386 in a oval. The barrels of milled receiver MAK-90 and 91 rifles are not threaded. The fit and finish of Poly Tech rifles pre or post ban are the best of all Chinese rifles imported.