Unusual thread

I have come across an unusual thread on an early 1900's (I guess) church candlestick.

The male is a steel rod 0.258" diameter with a pitch of 18tpi or 1.4mm.

I can't relate this to Whit, BSF, UNC or Metric standards - did the makers have their own exclusive one?.

Thanks.

Hmmm. It could just be a1/4 dia x 18TPi "AmericanStandard Straight Pipe Thread for Pressure Tight Joints." Strange but it might just be.

Interestingly 0.258" diameter is Number 2 AWG

... May, or may not, be relevant.

MichaelG.

I think you will find 1/4 ansi is for 1/2 OD pipe .

The nearest i could find is 1/4 x20 whit or 1/4 x 16 acme .

18 tpi is really odd at this size as far as i can see .

The only othe one was 17/64 but this is 26tpi as far as i could see .

Ian

1/4 pipe thread is like our BSP and refers to the bore, the OD for the american 1/4x18 pipe thread is 0.540"

There is an American ASME 16-18 thread that is 0.268" OD, 18tpi

J

I think MadMike is talking about American National NPSM or NPSL 1/4-18 straight mechanical threads, but the OD of those threads is .517 to .526, not .258" or 1/4" nominal.

I have never come across anything with a 1/4"-18 thread with a true .250 or close OD. The only threads common in North America with 18 tpi are 5/16"-18 UNC (.312" OD) and 1/4"-18 pipe threads (.520 to .540" OD or thereabouts) in the NPT, NPTF Dryseal, NPSM, NPSL, NPSC pipe thread systems.

For 1/4" OD, there are many tpi types in the USA based unified thread series, inluding 20, 24, 27,28,32,36,40,48 and 56 tpi, but NOT 18 tpi.

So, I can't say what it is, but I can tell you what it isn't....

Could be a custom turned thread done on a lathe, they can be any pitch and diameter.

JD

I have searched the web for an hour or so and found nil .

Jason , i can find no reference to 16-18 asme (which is ansi ).

I did find some reference on a website called Engineers edge that listed the smaller asme threads .

There were only references to the following thread dimensions relavent to this forum thread :

1/4-20 (or28) tpi maj dia .250"

5/16-18 maj dia .3125"

If this candle holder is that old it is possible that they had thread forming tools made and they would have used what was at hand and 18tpi is used in whitworth , maybe they had a tap and die made to suit the wire dia ?

Ian

With something craftsman made like a candlestick I think there's a fair chance that the threads were cut with hand chasers. They could be any diameter, just made to fit each other. I've got a couple of chasers but I've never actually tried cutting a thread with them. The internal thread would seem to be more difficult than the outer one but, hey, these guys were skilled.

Rod

16-18 ASME is 18 tpi 0.268" diameter so probably close enuf. ASME is (I think) American Society of Motor Engineers and are basically to American National standard form but covering a fair number of oddball sizes and pitches for automotive applications. Usually finer than AN versions, altho' not in this case.

So far as I'm aware the systems heyday was in the First World War and early post war period slowly petering out between the wars and in the post Second World War period save for a few examples which were kept in step with AN / UN thread size, form and specification evolution.

Newnes Engineers manual is the only UK book I'm aware of with a full ASME thread listing. Size designations are strange by modern standards as the number-thread system is used extending up to 30 which is 0.45" diameter. ANF / ANC number sizes are a subset of the ASME list which usually offers several choices of pitch for each size rather than the familiar coarse / fine pair. No 4 and No 8 have four choices each! Surprisingly not in Machinery's Handbook or World Screw Threads Guide.

Clive

can I recomend the data sheet by andy pugh link I converted This to Excel And find reverse lookups of threads invaluable

btw nearest match I find is 16-18    ASME

Edited By jason udall on 15/12/2012 00:12:55

Thanks very much for all the replies.

Each candlestick is made up of about 9 separate decorative brass rings (ie short tubes) of differing diameters. These locate with each other and, together with the large base, are pinched up by a steel rod up the middle that is threaded for a short distance at each end. The bottom thread screws into the base and the top one into the tube that holds the candle - a simple collection of polished fancy rings with a rod up the middle. There are six of these standard-looking candlesticks and I guess that all of them are the same thread. They are not 'one-offs' I am fairly sure.

The steel rod is not truly round and looks pretty rough so perhaps they are older than I think. Of course, for all their lives they have been standing in a cold and damp church. Perhaps the rod began life at 0.250" but that still wouldn't explain the 18 tpi.

Thanks again.

.

Looks like my posting crossed with yours..

the modular nature of these candle sticks reminds me of a description of a church "furniture" designer catalogue of the late victorian era..can't think of name..

Having worked with a very experianced engineer in Yorkshire who did a lot of repair shop (machine work) at KWVR, he passed a little gem of information relating to odd sized whit threads being linked to repair work on fire box components (if I remember correctly). He mentioned it as I had been trying to identify an odd whit like thread but with the wrong diameter and I am certain it was 18 or 19 tpi but can't remember much else about it.

I mention this as it would possibly be around the right time historically and if you are in an area that had links to steam engine repairs etc. it might be part of your answer.

Mark

Clive that is the tread I was thinking of, only standard that is near.

I use the online version of the list Jason posted quite often. I also had another good one for US threads but seems to have disappeared.

J

Edited By JasonB on 15/12/2012 07:53:36

I stand corrected !

Just goes to show how useless search engines can be !

I must have typed in asme a hundred times in every way i could think of and it still lead me to the same location with the same useless information.

I wonder if there are any books written about these old and obsolete thread forms and thier history ?

Something like this would make a good ongoing article in MEW .

Ian

> Something like this would make a good ongoing article in MEW .

I am somewhat disturbed to realise I agree with you!

"A History of Screw Threads in Forty Five Parts" to be followed by a similar series on nuts and internal threads, just for completeness

In all honesty though, the story of the mundane or simple can often be more fascinating. What could be simpler than water out of a pipe, but think of all the stories associated with that?

Neil

Much debate about am old thread, so why not ignore the interwebbynet and/or todays thread reference charts etc. The thread described exists as an old American standard thread designed to provide a tight joint in pressure joints. In order to find this you will need to go back in time. It is clearly described and explained in th "Machinery's Handbook". However I found it in the 13th edition from 1948. The theory appears to be that it is designed for use whwere ond component was made from a ductile material, the female thread would be slightly tapered and thus when the bolt/stud was tightened the metal would deform and not only go tight but would also provide a "pressure tight joint". This may have been used on the canle sticks to get tight joints whilst not having precise dimensions.

Thread diameter 0.258 inches? That would be a good old quarter of an inch in anybody's money. A increase in diameter of a mere 0.008 would be possibly due to a worn die used on "oversize stock" or simply the result of rolling the thread. HTH.

Are we too obsessed by our DROs, micrometers and digital calipers and using nice clean BDMS?
A victorian brassworks would have considered a dimension holding 8 thou accuracy to be high precision. Their lathes wouldn't have had dials at all and the workers would have measured dimensions with calipers against their wooden rulers though the forman would have perhaps had a precious brass rule marked in 64ths.

I go with the rod being 'best quality' black iron rod and the theads chased as mentioned above.

Or the Manchester plumbers thread which was used by manchester plumbers and was any size you wanted but it had to be 20 tpi.

Perhaps with Bolton being further north all their plumbers used 18 tpi ?

John S.

I don't think it would warrant a full page but was thinking more along the lines of something that used to appear in the early MEW issues .

Every so often there would be helpful hint or quick tip added to one of the pages and i guess it helped as a page filler as well .

Maybe MEW could have a "did you know " sort of thing added here or there and a couple could be taken from this forum thread alone , asme and manchester plumbers .

I'm sure the scribe a line section would be running hot with arguments from every angle !

Ian