Identifying Pipe Threading Head Thread

[bsf]

Thank you in advance for your time. Do you have any suggestions for identifying the thread for unmarked dies in manual ratcheting pipe threading die heads? Highly unlikely to be anything but NPT or NPSM.

I have a full set of old, Ridgid 12-R die heads: 1/8”-2”. However, the individual dies are not marked on the outside edge where newer dies are stamped w/ identifying info. I only know the nominal pipe size, but not the thread. Within a nominal pipe size, I believe different thread dies all use the same 12-R head. Based on some old sets of card packaged dies I have, it appears some of the old dies were not explicitly marked with thread. It may have only been indicated by a code on the packaging. Given the source of the dies, I suspect they are NPT, but some NOS NPSM dies were also found associated w/ the mentioned 12-R die heads. It is not recommended to R&R 12-R dies w/o having a factory pipe ****** to assist in setting them, as there is play in the die holder slots. However, I am wondering if the only way to verify thread is to match the die heads with an NPT or NPSM factory ****** or fitting. I have easy access to some, but would have to source the rest. I have compared stamped, 2” NPSM & NPT dies, and I cannot distinguish between them without using the stamping. Any suggestions?

 

[PBCampbell]

If I am understanding your question correctly and I am going from memory, I don't recall the thread cutters being marked as to NPT or NPSM, just the TPI. It would take me a couple days at least to get to my manual stuff, but if you don't get a confirmative answer I'll check.

 

[bsf]

I have a bunch of Ridgid 12-R replacement die sets new in package, or unused and missing packaging. Some are stamped NPT. Some are stamped NPSM. Some have no stamping to indicate thread. TPI is not listed anywhere, but would be implied by nominal pipe size & thread. I am assuming none of the unmarked dies are API, BSPT, BSPP, or LH NPT. The small, Ridgid UNC & UNF bolt dies I have seen are indeed stamped w/ bolt diameter & TPI. I am primarily concerned with the dies already installed in the 12-R die heads. Based on the packaged replacement dies I have, it seems the dies in the heads are not marked w/ thread. So, I need to figure out a way to determine it.

 

[bsf]

Photo from Ridgid of 12-R die head.

 

[RTM]

Get a pitch gage, and measure them? TPI is TPI, isn't it?

Screw Pitch Gages

Screw Pitch Gages

nz.starrett.com

 

[bsf]

Get a pitch gage, and measure them? TPI is TPI, isn't it?

Screw Pitch Gages

Screw Pitch Gages

nz.starrett.com

For nominal pipe size, both NPT (National Pipe Tapered) and NPSM (National Pipe Straight Mechanical) have the same TPI.

 

[OccupantRJ]

Take one cutter from the die head. Take the unknown cutter and place them point to point on a flat surface, but flip one over. Mesh the threads. If the alignment is straight, they have the same taper. With one straight and one tapered, the alignment will be off.

 

[bsf]

Thank you everyone. I have the dies identified. They are all NPT. I inspected all die heads again, and 2”, 1-1/2”, & 1-1/4” all have “newer” dies that are indeed labeled NPT. My prior inspection was obviously not very thorough. The dies in the other 6 – heads (1/8” – 1”) are not marked with thread type. The taper on NPT threads is only 1º47”. However, setting the 3 – largest die heads, known to be NPT, on a flat, horizontal surface with a vertical reference, I was able to visually discern the taper. I used a straight edge placed on the teeth on opposite dies in a head and compared to the vertical reference. This made the taper much more noticeable to me, and I could reliably repeat this crude test to verify a taper. Then, I used the same method to determine all the other die heads had tapered thread dies installed. Then, to obtain final confirmation of the unmarked dies being NPT, as opposed to the unlikely British Standard Pipe Taper, I screwed known NPT/NPSM ******* or pipe plugs into the smallest 6 – die heads to verify correct TPI. I did not have to remove any dies from the heads to determine them NPT.