1. Use the open internal and external circle structure,and with screw fixed.It is effectively to solve the problem that when small diameter solft tube connect the hared tube,it is easy appear dead angle,and liquid or gas leakage problem. 2. Edge is no burrfree,it is ability to prevent the tube damaged 3. By a efficiently hydrogen relief treatment,long-term use needn't to worry fracture and other problems 4. Accord with DIN3017 Standard.By 48 hours salt and fog test,it has a good corrosion resistance 5.By last 36 hours elastic test,to insure a high strength mechanical properties.