The Retro Arms CNC AK Hop Chamber is a superb axample of a company getting it right. 
Precisely machined from Duralumium, this unit is strong and reliable. 
The collet locking nut allows the barrel to stay totally locked to the hop chamber with no rotation or vibration. 

Compatible with virtually all aftermarket nubs and hop rubbers, we generally pair this unit with our custom flat nub and PDI W-Hold hop rubber.