American Heathkit thread sizes ? - UK Vintage Radio Repair and Restoration Discussion Forum

tim.norris · 6th Apr 2019, 1:44 pm

I am just finishing off rejuvinating a American Heathkit IT12 Signal Tracer . looking to replace some of the chewed up screws but am a bit perplexed as to what threads some of the screws are . obviously not metric or BA . what thread system did they use ? all help appreciated. Regardsl. Tim.

Ted Kendall · 6th Apr 2019, 2:06 pm

5-40, which is a thread I first encountered on Riko slot-car axles, is listed as the size of most of the small ones, for which the ubiquitous flanged screws for 3.5" hard drives seem to be a good substitute. Be nice to know the thread standard, though.

kalee20 · 6th Apr 2019, 2:09 pm

Almost certainly UNC or UNF.

tim.norris · 6th Apr 2019, 2:15 pm

Thanks for the replies . when i started in the motor trade 40 odd years ago unf and bsf were the popular sizes .now long gone . will have a look at the threads mentioned . Regards. Tim.

John KC0G · 6th Apr 2019, 2:19 pm

Tim, the threads will be UNC (unified coarse) or possibly UNF (unified fine), which are the standard threads here in the USA. A search containing the words "UNC" UNF" and "threads" will get you more information.

The Unified Thread Standard was adopted by the USA, UK and Canada in 1949, after the interchange issues in WW2. The prior USA standard screws, nuts and bolts were compatible with the new standard. My understanding is that some of the tolerances changed.

At my local hardware store nuts and bolts in the bins upto #8 are UNC only. #10 and some larger ones are available in UNC and UNF. A diameter gauge and thread gauge (turns per inch) are good things to have.

73 John

6AL5W-Martin · 6th Apr 2019, 3:53 pm

german metric screws are mm, the cut is 60 degrees.
english screws are turns per inch, the cut is 55 degrees.
Uncle Sam screws are english screws, but with the 60 degrees cut.

Heathkit was allover the same, our heathkits here in germany have UNC screws.
But english heathkits are a special one, they have another front plate ( compare VTVM to VVM ), and english screws.
So the question is: is the apparatus made in UK or not?
Martin

David G4EBT · 6th Apr 2019, 3:53 pm

Being American I think the threads will be either UNC or UNF - 'Unified National Fine' or 'Unified National Coarse'. Other less likely possibilities are UNEF - Unified National Extra Fine', or 'Unified National Special'.

These tables of information at the links below might help. The one at this first link outlines the history of 'Unified National' threads, which dates back to WW2, when the differences between American and British thread forms became a problem, especially in manufacturing and repairing airplane engines. Shortly after the war, (1948) representatives of Britain, Canada and the United States agreed on a Unified Standard:

https://www.sizes.com/tools/thread_american.htm

This might also be of interest:

https://www.fullerfasteners.com/tech...ican-standard/

Ooops, crossed with other posts.

tim.norris · 6th Apr 2019, 8:02 pm

Martin . its the American version. David .thanks for the informative reply .hope your well i`m just sorting the probe at the moment . i remember when you turned the new red end for me that the thread for the probe tip was an oddball one . Thanks again. Tim.

David G4EBT · 6th Apr 2019, 8:49 pm

Quote:

Originally Posted by tim.norris

Martin . its the American version. David .thanks for the informative reply .hope your well i`m just sorting the probe at the moment . i remember when you turned the new red end for me that the thread for the probe tip was an oddball one . Thanks again. Tim.

Yes, the 'mystery thread' size for the metal tip, had us foxed - I knew being American it would be an imperial size - not metric. I have a chum who runs a light engineering firm - just as 'one man band', so I sought his help. It turned out to be 1/4" x 32 TPI 'Model Engineering' thread. I didn't know there was such a thread, but he did, and more importantly, he had a tap. Looking at the chart at the link I posted earlier, I think given that the probe was American and 32 TPI, was most likely 1/4" UNEF. (Unified National Extra Fine).

Come what may, the metal tip fitted the acetal 'red nose'.

Like all Heathkit stuff, the 'IT12' is a nicely designed signal tracer, and will earn its keep.

Every good wish in completing the restoration Tim.

emeritus · 6th Apr 2019, 11:00 pm

My understanding is that the US only standardised on what are now essentially the unified thread standards in the late 1930's - before this there were numerous proprietary standards offering ranges of pitches for each size, and a larger range of intermediate sizes, including sizes designated by numbers instead of fractional inches for sizes greater than 1/4", and even in 1942 the domestic use of Unified threads was by no means universal: see the attachment of post #8 of this thread:

https://www.vintage-radio.net/forum/...10#post1125210

The avioniocs and military radio stuff being manufactured by Plessey in the early 1970's used unified threads, although we were using ISO-Metric threads for new designs. Not all customers wanted them: when proudly demonstrating the metricated version of some radio equipment for use at airfields, several European customers asked for them to be supplied in the old design of cases with Unified threads: all their existing stuff used that standard and they didn't want the hassle of having equipment with two incompatible standards of fastener.

We only used the "Even" UNC and UNF sizes. What with the presence of the older BA screws in the lab's engineers' rummage drawers, I soon became adept at recognizing whether a fastener was BA, UNC, UNF or Metric just by looking at it.

I never met anything that used 5-40 UNC, but my copy of Machinery's "Guide to World Screw Threads" indicates that it is virtually identical with 1/8" Whitworth, other than the thread flank angle.

I have more UNC screws and nuts in small sizes (even sizes only, 0-80 UNC up) than I will ever use, mostly steel, pan head. PM me with what you need, and if I have the sizes I will stick some in the post, FOC.

Herald1360 · 6th Apr 2019, 11:45 pm

As Emeritus says, 5-40 (UNC) is the thread in question. The 5 is the screw gauge (diameter) and the 40 is the threads per inch (thread pitch). It's not a very common screw size though some are available on Ebay.

tim.norris · 9th Apr 2019, 7:22 pm

Emeritus. thanks for the offer will let you know if i need any . many thanks . Tim.

6th Apr 2019, 2:06 pm	#2
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,675	Re: American Heathkit thread sizes ? 5-40, which is a thread I first encountered on Riko slot-car axles, is listed as the size of most of the small ones, for which the ubiquitous flanged screws for 3.5" hard drives seem to be a good substitute. Be nice to know the thread standard, though.

6th Apr 2019, 2:09 pm	#3
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: American Heathkit thread sizes ? Almost certainly UNC or UNF.

6th Apr 2019, 2:15 pm	#4
tim.norris Hexode Join Date: Feb 2012 Location: Blackburn, Lancashire, UK. Posts: 282	Re: American Heathkit thread sizes ? Thanks for the replies . when i started in the motor trade 40 odd years ago unf and bsf were the popular sizes .now long gone . will have a look at the threads mentioned . Regards. Tim.

6th Apr 2019, 2:19 pm	#5
John KC0G Hexode Join Date: Mar 2009 Location: Minneapolis, Minnesota, USA. Posts: 279	Re: American Heathkit thread sizes ? Tim, the threads will be UNC (unified coarse) or possibly UNF (unified fine), which are the standard threads here in the USA. A search containing the words "UNC" UNF" and "threads" will get you more information. The Unified Thread Standard was adopted by the USA, UK and Canada in 1949, after the interchange issues in WW2. The prior USA standard screws, nuts and bolts were compatible with the new standard. My understanding is that some of the tolerances changed. At my local hardware store nuts and bolts in the bins upto #8 are UNC only. #10 and some larger ones are available in UNC and UNF. A diameter gauge and thread gauge (turns per inch) are good things to have. 73 John Last edited by John KC0G; 6th Apr 2019 at 2:19 pm. Reason: typo

6th Apr 2019, 3:53 pm	#6
6AL5W-Martin Hexode Join Date: Nov 2006 Location: Biedenkopf, [Hessen], Germany. Posts: 425	Re: American Heathkit thread sizes ? german metric screws are mm, the cut is 60 degrees. english screws are turns per inch, the cut is 55 degrees. Uncle Sam screws are english screws, but with the 60 degrees cut. Heathkit was allover the same, our heathkits here in germany have UNC screws. But english heathkits are a special one, they have another front plate ( compare VTVM to VVM ), and english screws. So the question is: is the apparatus made in UK or not? Martin __________________ www.wellenkino.de Vintage Scope restorations

6th Apr 2019, 1:44 pm	#1
tim.norris Hexode Join Date: Feb 2012 Location: Blackburn, Lancashire, UK. Posts: 282	American Heathkit thread sizes ? I am just finishing off rejuvinating a American Heathkit IT12 Signal Tracer . looking to replace some of the chewed up screws but am a bit perplexed as to what threads some of the screws are . obviously not metric or BA . what thread system did they use ? all help appreciated. Regardsl. Tim.

6th Apr 2019, 3:53 pm	#7
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,767	Re: American Heathkit thread sizes ? Being American I think the threads will be either UNC or UNF - 'Unified National Fine' or 'Unified National Coarse'. Other less likely possibilities are UNEF - Unified National Extra Fine', or 'Unified National Special'. These tables of information at the links below might help. The one at this first link outlines the history of 'Unified National' threads, which dates back to WW2, when the differences between American and British thread forms became a problem, especially in manufacturing and repairing airplane engines. Shortly after the war, (1948) representatives of Britain, Canada and the United States agreed on a Unified Standard: https://www.sizes.com/tools/thread_american.htm This might also be of interest: https://www.fullerfasteners.com/tech...ican-standard/ Ooops, crossed with other posts. __________________ David. BVWS Member. G-QRP Club member 1339.

6th Apr 2019, 8:02 pm	#8
tim.norris Hexode Join Date: Feb 2012 Location: Blackburn, Lancashire, UK. Posts: 282	Re: American Heathkit thread sizes ? Martin . its the American version. David .thanks for the informative reply .hope your well i`m just sorting the probe at the moment . i remember when you turned the new red end for me that the thread for the probe tip was an oddball one . Thanks again. Tim.

6th Apr 2019, 11:00 pm	#10
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,349	Re: American Heathkit thread sizes ? My understanding is that the US only standardised on what are now essentially the unified thread standards in the late 1930's - before this there were numerous proprietary standards offering ranges of pitches for each size, and a larger range of intermediate sizes, including sizes designated by numbers instead of fractional inches for sizes greater than 1/4", and even in 1942 the domestic use of Unified threads was by no means universal: see the attachment of post #8 of this thread: https://www.vintage-radio.net/forum/...10#post1125210 The avioniocs and military radio stuff being manufactured by Plessey in the early 1970's used unified threads, although we were using ISO-Metric threads for new designs. Not all customers wanted them: when proudly demonstrating the metricated version of some radio equipment for use at airfields, several European customers asked for them to be supplied in the old design of cases with Unified threads: all their existing stuff used that standard and they didn't want the hassle of having equipment with two incompatible standards of fastener. We only used the "Even" UNC and UNF sizes. What with the presence of the older BA screws in the lab's engineers' rummage drawers, I soon became adept at recognizing whether a fastener was BA, UNC, UNF or Metric just by looking at it. I never met anything that used 5-40 UNC, but my copy of Machinery's "Guide to World Screw Threads" indicates that it is virtually identical with 1/8" Whitworth, other than the thread flank angle. I have more UNC screws and nuts in small sizes (even sizes only, 0-80 UNC up) than I will ever use, mostly steel, pan head. PM me with what you need, and if I have the sizes I will stick some in the post, FOC. Last edited by emeritus; 6th Apr 2019 at 11:07 pm.

6th Apr 2019, 11:45 pm	#11
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: American Heathkit thread sizes ? As Emeritus says, 5-40 (UNC) is the thread in question. The 5 is the screw gauge (diameter) and the 40 is the threads per inch (thread pitch). It's not a very common screw size though some are available on Ebay. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

9th Apr 2019, 7:22 pm	#12
tim.norris Hexode Join Date: Feb 2012 Location: Blackburn, Lancashire, UK. Posts: 282	Re: American Heathkit thread sizes ? Emeritus. thanks for the offer will let you know if i need any . many thanks . Tim.