Mystery screws

Feb 28, 2015 15 Replies
C

I bought an old lamp and rewired it. Not sure of the age or origin, but it looks Art Deco. Here are some pictures:

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I had to remove the screws to rewire the lamp. Some of the screws were hard to remove and the slots got damaged. Now I'd like to replace the screws, but they're a really weird size. Here are the details:


- Brass screw, slotted round head



- Length: 8 mm



- Diameter: 3.70 mm



- Pitch 0.78 mm (as best as I can measure)



Here's what they aren't (because I've tried and they don't fit):


- #6-32 UNC



- #8-32 UNC



- 5/32" British Standard Whitworth



- 4 BA



- M4



For now, I've reassembled the lamp with the original screws. However, it bugs me that I can't identify the originals. Am I missing an obvious size?



Best wishes,



Chris


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D

On 02/28/2015 3:31 PM, Christopher Tidy wrote: ...

...

I notice you've listed no numbered UNF in the above...that'd be my firstest guess sight unseen...

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C

All the UNF pitches looked too fine. These are pretty coarse screws.

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J

There are some "deprecated" UN threads that haven't peen seen in ages. A couple I know off the top of my head are 6-48 and 12-32.

The 6-48 is common on guitars.

Jon

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T

Common on scope mounts too .

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D

Looking on the internet at screw threads, it looks like 6-32 is a little small and 8-32 a bit large. But the pitch is real close.

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This site has screw dimensions in both inch and metric.

Dan

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D

Well ... first off -- the pitch he measured is within 1.7 % of a

32 TPI thread, and given the stated uncertainty of that pitch measurement, it quite likely *is* 32 TPI.

However, the diameter is a bit large. 6-32 should be a 0.138" clearance hole, and what he has is a bit fatter than that. But I'm not sure about the diameter being any particular standard number size. Some manufacturers in the US were using non-standard proprietary threads just to keep a captive market.

Any clue as to where the lamp came from? Given the wide range screws that he tried, I suspect that the lamp is currently in the UK. :-)

Enjoy, DoN.

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B

Have you explored the BA thread charts (British Association ) commonly used on electrical equipment in the wayback days.

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J

The standard for M4-0.7 is very close at Max Dia - 3.978 and Min dia -

3.838, pitch is 0.7mm.

It could be simply non-precise manufacturing as I've noticed that say

6-32 screws out of electrical appliances often seem slightly smaller then standard.
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C

It's currently in Germany. I bought it from a guy here, but know nothing mo re about its origin. The lampholders use an Edison screw (E27).

I did wonder if the thread was M4 x 0.8 mm. Apparently this thread exists, but is extremely rare. But I haven't been able to find an M4 x 0.8 mm screw to try out the theory.

Chris

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B

On 3/1/2015 6:43 AM, Christopher Tidy wrote: ...

You could turn a short length of M4 x .8 to test. .8 should be a pitch available on your lathe - it's the standard/coarse M5 pitch.

Bob

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L

Got a lathe and the proper gearing? Make one to try!

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C

In England, yes. Here, sadly not.

Chris

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M

An accquaintance of mine does old lamps. He say 8-40 is a standard on those. 32 and 40 tpi were standards not much used today.

CP

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L

MOP CAP fired this volley in news:2015030110215814330- email@domaincom:

8-32 not much used? Really? Lloyd
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