I'm looking to get 2 1/2" dies for my Ridgid 4P threader. I see dies for other threaders, such as Toledo, going for much lower prices. I'm wondering if direct substitution or substitution with shims is possible. I don't want to try precision machining the dies. However, I can't seem to find the dimensions of the various manufacturers dies anywhere online. Does anyone know of a source? Just for the record the Ridgid 4P dies are ~621.5mils parallel to the threads and ~747.9mils perpendicular to the threads.

Welcome to the TT forum.   Sorry i can't answer you question, but maybe someone out there knows.   

I welcome you also, and also have no answers for you. I bet someone will come along soon that knows.

I am of no help either except to welcome you.

2½" -8" have the same threads.  8TPI, tapered at 3/4"/ft  (or 1/16"/inch)

Those threaders use one size of dies and cut 2½", 3", 3½", and 4" pipe threads.

We still run into 3½" pipe.

We would use them on the pipe clamped in a pipe vise.  The power was supplied through a bar about 6' long with 2 u-joints, with the other end in a 300 machine.

Old fitters would talk about being careful because if the bar with the u-joints  bound up it would flip the power machine, the vise with the pipe or both. The mayhem would stop when the set-up had flipped far enough away to pull the cord. 

Now all the power machines have foot pedal switches.

Chilly