8-32 screw oddball

[Susquatch]

My bride needs a short length of screw for a light fixture. There are four of them each around 1.5" long.

My thread gauge, and screw fitter both say that it's an 8-32. I have tone of 8-32 Screws in my screw collection.

However, none fit. They are all slightly too big. The originals don't match up with anything else on the screw charts.

Does anyone know if there is something special about the screws used in light fixtures? Is there something like a #7.5-32 screw?

Before anyone else suggests it, I broke an 8-32 die trying to clamp it down tight enough to recut an 8-32 to fit. It just snapped in half. It just became a very expensive screw......

Next up is single point threading on the lathe...... LOL!

 

[Darren]

4mm, 0.80 pitch is probably what you need, although 0.7mm is standard for 4mm.

 

[Susquatch]

4mm, 0.80 pitch is probably what you need, although 0.7mm is standard for 4mm.

My very first thought was that it is metric but it would not fit any of my metric screw gauges. I'll have to see if I can find 0.8

 

[Former Member]

I have tone of 8-32 Screws in my screw collection.

I know what your problem is......you are using musical screws.

 

[PeterT]

I've had the same frustrating issue on light fixtures & related electrical. I don't have the answer. They are definitely pre metric. They look like crudely rolled threads. They seem to fit their crudely tapped holes in fixtures, junction boxes etc. but apparently nothing else in the mechanical world. Good luck.

 

[Dabbler]

I've run into this more than once. All electrical screws that are *nominal* for a size and pitch have evolved into something quite different. I have stopped fighting this and buy extra screws from electrical wholesalers instead of using 'standard' ones...

What I think you have is an actual electrical 8-32 (But I thought they were supposed to be 8-40), but .020 undersized... If you are missing the screws, it is hard to check the OD and pitch....

For instance the screws for pulling a duplex socket into the box are undersized by about .012 or so... very frustrating (and yes that tool that rethreads those holes with about 4 threads in one tool are undersized as well).

 

[Tom O]

I’m not sure what size it is I have one of those screwdriver with 2 size taps built in for reclaiming electrical threads.

 

[Dabbler]

I have one of those screwdriver with 2 size taps built in

That's what I was referring to - My screwdriver tap sizes are smaller than my Cleveland ones of the 'same' size...

 

[Former Member]

Its either a 4-0.70 or 4-0.75 if metric. If its a European light definitely metric, Ikea metric otherwise I agree with @Tom O on just tap it out and be done with it.

 

[little ol' e]

Could be a 6-32 tapped hole

 

[Susquatch]

Thanks all. I have found some screws that fit. Got them at a lighting place. They are called 8-32 on the package but they are grossly undersized.

I think @PeterT & @Dabbler are probably right about the history of this.

Btw, @Dabbler, I did have 3 other screws I could use as gauges. They fit an 8-32 gauge but quite loosely. Same went for fitting an 8-32 nut. They are just a smaller OD. I was just missing one. So at least I had something to measure from and compare.

The guy at the lighting shop instantly knew what I was talking about. But he took the view that only the lighting folks have true 8-32 Screws. It's everyone else who is wrong and makes them too fat! LOL!

So much for standards.

Now I just have to replace my broken die.

 

[Former Member]

Thanks all. I have found some screws that fit. Got them at a lighting place. They are called 8-32 on the package but they are grossly undersized.

I think @PeterT & @Dabbler are probably right about the history of this.

Btw, @Dabbler, I did have 3 other screws I could use as gauges. They fit an 8-32 gauge but quite loosely. Same went for fitting an 8-32 nut. They are just a smaller OD. I was just missing one. So at least I had something to measure from and compare.

The guy at the lighting shop instantly knew what I was talking about. But he took the view that only the lighting folks have true 8-32 Screws. It's everyone else who is wrong and makes them too fat! LOL!

So much for standards.

Now I just have to replace my broken die.

I guess you found the right "tone".

 

[Janger]

Do they go way back and are somehow a british standard? Or something else strange - Westinghouse 8-32? Edison 8-32? I did some googling and couldn't find anybody talking about this.

 

[Dabbler]

I don't think so. I think it was more like:

1.. we need a thread that is very fine. Oh! use 8-32.
2.. Sometimes it gets stuck and cross threaded = solution. some clearance.
3.. a few years later - this is too sloppy. Let's close the thread a little
4.. see 2..
5.. see 3..

iterate until ridiculous..

 

[Susquatch]

@Janger

I think @Dabbler described it well. The lighting guy sure knew the difference.

But perhaps I can add a nuance.

Many of the screws on a lighting fixture are installed by hand and either have friction heads (think knurled but much less sophisticated) or they have little knobs (tiny balls with a threaded hole). The screw I was after uses a knob.

A very loose fit would facilitate hand installation.

Come to think of it, even the ones that need a tool to tighten them have crummy tool interfaces that would benefit from a loose fit.

I think lighting fasteners are mostly junk. The folks who do lighting for a living probably think the rest of us use junk.

 

[140mower]

I think lighting fasteners are mostly junk. The folks who do lighting for a living probably think the rest of us use junk.

Those poor buggers are like a calf that's born against the electric fence........ They just don't know that it's wrong....

 

[little ol' e]

I usually run about 2500 of these per month.
1st stop is laser then tap 6-32 then onto forming.
These are for residential homes.
Pretty sure these haven't changed over the years but... ya never know.
Good to hear you found a screw that worked Susquach.
These are the parts below. See how the hole was lasered to .106 +/- which is same as #36 drill for 6-32 thread.
Just in case any electrical guys would like to know as well.

 

[Janger]

Ah ha the plot thickens! Those screws might be #6 not #8! Susquatch check if they go in a #6 nut?

 

[Susquatch]

Ah ha the plot thickens! Those screws might be #6 not #8! Susquatch check if they go in a #6 nut?

Not even remotely close......

Size wise, they are more like a number 7.5. If you are interested in more details, here are a few numbers. I'll call the ones I have a #L for light screws

Here is a chart

OD
#6 0.1406
#L 0.1505
#8 0.1563
Metric mm
4 0.1575
3. 0.1181
3.5 0.1378

 

[PeterT]

Everything that I searched on the WW interweb says #6, #8, #10 32 TPI for N-Am electrical.
I can see how old fixtures violated by a previous handy-man (or handy-woman) may not fit properly. So the only logical conclusion seems to be loosey-goosey quality control because I know some brand new fixtures from Big Box Hardware did not fit my fasteners. I figured maybe we went metric there too when I was delirious with Covid.

406.5 Receptacle Mounting.

The machine screws that come with the receptacle should be used.

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