View Full Version : Strange Thread: PG7

Paul Alciatore
06-17-2004, 10:59 PM
Anyone ever heard of a thread called a PG7? It is on a plastic strain relief/entrance pigtale for a power cord on some studio lights. It seems to be close to 1/2-28 but is actually a little smaller in diameter. I have a dozen of these lights and they have all been assembled with 1/2-28 nuts and they are all stripping off. Only about 0.005" of thread engagement.

I believe I have a box of matching nuts comming from the manfacturer (www.heyco.com) so I don't need help finding them, I'm just curious as to what the heck they are and why in all creation did they use such an oddball size. There seems to be a whole series of PG threads as they list others - different diameters I guess. Anybody ever heard of them?


Paul A.

Spin Doctor
06-17-2004, 11:02 PM
The reason they would use such an oddball size or pitch is called "BUY OUR PARTS"

06-17-2004, 11:37 PM
They wouldn't be 12 millimeter, would they. It's 0.7 millimeters smaller in diameter than 1/2".

John Stevenson
06-18-2004, 07:06 AM
Yes Paul,
They are getting quite popular over here to replace conduit threads which here have always been metric.

Somewhere on line I have seen the specs but can't remember where.
J&L do taps for the PG series but they are mega $$$$
I shop carefully for fittings and try to avoid these are there isn't the range of fittings yet for PG as there is for conduit.

Some of our new motors come with plastic terminal boxes with PG in them but we drill out and retap conduit.

Experianced electricians here call them PiG threads.

Found the spec sheet

They recommend 1/2" x 20 UNF for PG7 [ at the bottom ]

John S.

[This message has been edited by John Stevenson (edited 06-18-2004).]

Paul Alciatore
06-18-2004, 12:22 PM
Thanks John,

So it's a 0.49-20 thread. It looks like it is being used in the cable fittings industry as some sort of "standard" there.

The Sealcon site's specs say it "fits" 1/2-20 UNF but this is not really correct. The nuts in my fixtures must be 1/2-20 and they do "fit" but there is so little thread engagement that they strip out with the slightest force. I'll bet the manfacturer of my lights read a similar statement and just bought cheaper UNF nuts.

It sounds strange that it would be replaceing metric threads as I thought that the whole world was supposed to be going metric instead of vice-versa. I have a feeling that we will never see a single system of measure.

This just reconfirms what I have felt for a long time, EEs do NOT understand mechanics just as MEs do not understand electronics. It's a rare bird (like some of us) who can actually function well in both worlds.

Paul A.