Question concerning old metal octagons

[mark32]

Hello,

I came across one of those very old tiny round metal boxes, the kind with the threaded stem jutting up from the center of it. I'd like to know what size that thread is. Would it be the same as a 3/8 IP nipple?

 

[Buck Parrish]

Hello,

I came across one of those very old tiny round metal boxes, the kind with the threaded stem jutting up from the center of it. I'd like to know what size that thread is. Would it be the same as a 3/8 IP nipple?

I'm not sure the size but that stem in the middle is called a hicky. It counts as a box fill deduction.

 

[mdshunk]

Yes, 3/8ths iron pipe thread.

EDIT... the more modern regular fixture all-thread is 1/4th inch iron pipe thread.

 

[al hildenbrand]

The threaded stud is a carry-over from the days of gas lighting.

The common lamp was supplied with a 3/8" black pipe gas line that had normal pipe threads. All the fittings that gas light fixtures were made of were ported over to electrical luminaires. Eventually the pipes weren't used, but the threading and the sizing of the fittings remain unchanged to this day.

So, unless this particular box was intended to carry a very heavy (uncommon) luminaire, the stud is 3/8" NPT.

 

[mark32]

Thank you for the helpful responses. Even though I used I.P. in my post I didn't know what it meant, now I see it stands for iron pipe, thanks.

 

[LarryFine]

We always called the part that let you get the wires out of the nipple the hickey, as labeled here (although they didn't use it for that purpose here):