Threading Dies, 1/4 IP Pipe

[jmellc]

Repaired a couple of pendant lights recently, using 1/4 IP lamp pipe nipples I cut to length. That reminded me of a job where we tried to thread some downrods on similar lights. No die in the set was even close. I just checked several sites and found a tap on a lamp site but no die. From some charts I found, I gather the OD of the pipe is 1/2" and 27 threads per inch. I just saw a 1/2 x 27 die on Amazon. Has anyone else threaded this? I'd like to have the tools or at least the info for a similar job in the future.

 

[dfmischler]

So was this odd pipe size used with what was originally a gas lighting appliance? I have heard that a lot of that stuff was 1/8-27, not sure if it was NPT (tapered) or NPS (straight). You can still get dies for that size from Ridgid, etc. Not sure which head you would need to hold it. A commercial plumbing supply house could tell you what you would need. There are cheap 1/8-27 dies on ebay if you want to have one "just in case".

IIRC the standard NPT thread for 1/4" nominal pipe has 18 tpi. Remember that pipe threads have a standard taper, too, so a die made for machine screws (or conduit?) will probably not make up and seal properly with a pipe fitting. But you may not care as long as it works well enough to run wire through it.

 

[Fulthrotl]

Repaired a couple of pendant lights recently, using 1/4 IP lamp pipe nipples I cut to length. That reminded me of a job where we tried to thread some downrods on similar lights. No die in the set was even close. I just checked several sites and found a tap on a lamp site but no die. From some charts I found, I gather the OD of the pipe is 1/2" and 27 threads per inch. I just saw a 1/2 x 27 die on Amazon. Has anyone else threaded this? I'd like to have the tools or at least the info for a similar job in the future.

most likely it is 1/8" pipe thread.
but the stuff coming over from china could be most anything,
and even if you know what it is, the threads might very well
not pass with a thread gauge.

i'm suspecting that there is not a single thread gauge in the
entire PRC. i've seen 2" pipe that the couplings fall off of, and
it turns out that NEITHER the coupling nor the pipe thread is
cut correctly. same with locknuts. same with myers hubs.

i've gotten to the point where the bolts i attach lugs to bus
with, i use either 5/16"-18 or 3/8"-24 grade 8 allen head cap
screws, grade 8 nylocks, and grade 8 washers. i keep a box
of each in with my hypress terminals... and they are not chinese
made. you can torque a 3/8-24 grade 8 cap screw to the same
torque value as a 1/2" grade 5 coarse thread.

 

[electrofelon]

i'm suspecting that there is not a single thread gauge in the
entire PRC.

LOL so true. Happened to me recently: putting a locknut on an EMT fitting and finding the teeth wont even go through the paint before it skips out. These were UL listed fittings too.

That thread (assuming it corresponds to a standard) is likely a NPS/NPSM (national pipe straight/national pipe straight mechanical). Taps and dies are kinda hard to find but MSC has them.

 

[jmellc]

So was this odd pipe size used with what was originally a gas lighting appliance? I have heard that a lot of that stuff was 1/8-27, not sure if it was NPT (tapered) or NPS (straight). You can still get dies for that size from Ridgid, etc. Not sure which head you would need to hold it. A commercial plumbing supply house could tell you what you would need. There are cheap 1/8-27 dies on ebay if you want to have one "just in case".

IIRC the standard NPT thread for 1/4" nominal pipe has 18 tpi. Remember that pipe threads have a standard taper, too, so a die made for machine screws (or conduit?) will probably not make up and seal properly with a pipe fitting. But you may not care as long as it works well enough to run wire through it.

No this is a pendant light, with stem instead of cord. Stem goes down to a coupling and light couples to the bottom with a nipple. I bought replacement nipple at Home Depot, 1/4 IP size.