1)100% fit to Ridgid 300,500,535 Rex R50 threading machine 2)many heads available 3)casting steel made 815A Universal Self Open Die Head NPT, Right Hand 1/8" - 2". It is 100% the interchangeable to RIDGID 97075 815A. PART #: 97075 Weight: 6Kgswe supply dies head for Ridgid threading machines such as 300, 300C,535, 1233,1244 etc. Threading machine Dies Head(815A Self Open)