Model B - what thread standard?
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=172002
Printed Date: 13 Oct 2025 at 7:48pm
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Topic: Model B - what thread standard?
Posted By: ZWHO
Subject: Model B - what thread standard?
Date Posted: 13 Jun 2020 at 4:16pm
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Hi all, Very simple newbie question here. I've got a 1943 Model B, can someone tell me what thread type is used for the fasteners? I'm not used to old US machinery and am more familiar with British Standard thread. Particularly I'm interested in the thread for the wheel rim cam bolts. Thanks!
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Replies:
Posted By: steve(ill)
Date Posted: 13 Jun 2020 at 4:47pm
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The USA uses a US Standard Coarse Thread for most parts on the tractor.. We measure in INCHES also, but had a different thread pitch for some sizes.... The bolts thru the cam brackets should be 5/8 inch NC ( national course).. ------------- Like them all, but love the "B"s. |
Posted By: steve(ill)
Date Posted: 13 Jun 2020 at 4:51pm
Most external bolts would be NC - national course.... internal to the engine and trans might be nf - national fine........ below is a table.... 1/4 - 20 would be 1/4 inch diameter bolt, 20 threads per inch. ------------- Like them all, but love the "B"s. |
Posted By: frnkeore
Date Posted: 13 Jun 2020 at 5:52pm
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The US and UK thread forms are not the same but, should be interchangeable. When WWII started, or just before, they specified that they would interchange. The Brit was 55 deg angle, with a radius top, the US is 60 deg, with a flat top. So, any of your pre-metric bolts and nuts, should work. ------------- Frank 1959 D17 Series I #24001+, '59 D14 '55 & '59 Ford 850 & 861 Ferguson TO 35 Deluxe, Oliver 70 and 5 more. |
Posted By: steve(ill)
Date Posted: 13 Jun 2020 at 6:39pm
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Not a real good idea to interchanged the BSW and UNC bolts and nuts. They do have the same thread pitch ( most), but the angle is important... British and Americans noted this when we were in WWII and the BRITISH started to change THEIR STANDARD to match the USA parts.... War was over in a few years and not completely changed on their part.. They changed because it was not a good idea to mix and match bolts and nuts.. You cant get the same torque and holding power.... might be OK to hold the hood on, but i would not use on the axles or engine mounts.
------------- Like them all, but love the "B"s. |
Posted By: frnkeore
Date Posted: 13 Jun 2020 at 6:47pm
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Steve, your right. I had miss remembered that change. The change happened in 1949, when both the US & UK adopted the same thread profile. Even so, it would be hard to find, pre 1949 nuts and bolts, to use on that B. ------------- Frank 1959 D17 Series I #24001+, '59 D14 '55 & '59 Ford 850 & 861 Ferguson TO 35 Deluxe, Oliver 70 and 5 more. |
Posted By: steve(ill)
Date Posted: 13 Jun 2020 at 6:57pm
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Yea in the USA it would be very hard.. ZWHO is from the UK... I would imagine there are a lot of lathes, mills, machinery, trucks and things from the 1920- 40s that used the BSW thread that are still being operated... I dont know, but i would GUESS that you have a good choice of BSW, UNC and Metric threads available in England as they have changed their " standard" 3 times in the last 75 years............ In fact i think there are still some heavy machinery built that uses the BSW thread TODAY as they never did change ?? ------------- Like them all, but love the "B"s. |
Posted By: ZWHO
Date Posted: 15 Jun 2020 at 10:37am
| Thanks for the replies, very useful. Interesting to note the history of thread standardisation. |