Are you looking to replace your Harbor Freight tube roller drive axle with a keyed, high strength 4130 chromoly steel shaft, or over time have you fatigued and/or bent the SWAG drive axle? If you plan on using this shaft with your Harbor Freight dies, keep in mind that you will need to broach a 6mm x 3mm keyway in the three center drive dies to accept the 6mm x 6mm key stock. However, going from securing the center drive roller with set screws to using a key stock is well worth the investment and time.
When switching the drive roller to a keyed drive axle, the center drive roller will always move in a circular motion as opposed to the set screws that push the roller away from the drive axle on three sides. This creates an oblong circular pattern that naturally pushes your material you are rolling harder to one side causing the material to twist.