Tech Topics

The New England M.G. ‘T’ Register has a long history of providing its members with advice and technical expertise on the restoration and maintenance of our special cars. We present some of our favorite technical articles and tips here for members and visitors alike.

Whitworth - Metric - SAE
By: Steve Schultz
Steve gave a most interesting presentation on the technical aspect of the nuts and bolts used in our MGs over the years - in particular the standards to which the hardware was made - Whitworth - Metric - SAE. It covered both the history and technical specification of these standards.
In England in the early 1800's, there were no industrial thread standards. Every manufacturer had their own thread standard, which led to significant hardware problems. In 1841 Joseph Whitworth made a presentation to the "Institute of Civil Engineers" in England, proposing his "Whitworth Standard" for threaded fasteners, and it became the first "Standard" thread in England. It used a 55 degree angle of Pitch (the angle made between two threads) with rounded peaks and valleys on its threads.

Whitworth:
Comes in 3 configurations of British Standard Whitworth (BSW):
1. British Association (small threads),
2. 2. British Standard Coarse, and
3. 3. British Standard Fine.
SAE
It was developed by William Sellers around 1850 in the US. It was originally called the "Sellers Thread". The name was later changed to "American Standard Thread". It had a pitch angle of 60 degrees with pointed peaks and valleys on threads.
Whitworth and SAE thread standards came into particular conflict during WWII between the US and Britain, on compatibility and repairs of military equipment. The two then agreed to a compromise standard, and the "Unified Thread Series" was established. It was based on the US pitch angle of 60 degrees utilizing Whitworths rounded peak and valley radius on threads. Unified National Thread  consisted of both Unified National Course (or NC) and Unified National Fine (NF) threads. (Note: most bolt diameters have both a course and a fine thread designation, like 1/2 inch coarse - 20 threads/inch, or 1/2 inch fine - 28 threads/inch. Most automotive applications tend to use the fine thread. As a result, a British Standard Whitworth nut will fit a UNF bolt, except for the 1/2 inch size, although the fit is not a strong combination.
France, Germans, and Switzerland would not agree to this Unified National Thread standard (no surprise), and came up with their own "Metric" Standard. It used a pitch angle of 60 degrees, but metric dimensions and divisions. The winners in all this disagreement became Sears and Snap-On, who got to sell more wrenches to you and me!
-Tool wise, to help you identify your hardware, you can buy a set of "Thread Pitch Gages". It is like a small set of saw-tooth lingers, each one of a different pitch. When a particular finger's teeth perfectly matches the threads on a nut, bolt, or threaded hole, then that is the thread pitch you are dealing with. You can also buy templates with various hole diameters to determine what size (diameter) bolt you have.
Also, concerning BOLTS:
• The head of bolts may have "marks" on them. This designates their "hardness". No marks - probably made of recycled old Budweiser beer cans. 1ft here ire marks, count them up and "add 2" to the number, to determine the grade (don't know why - just do it). Grades range between 0 and S. with 8 being the hardest and "0" the softest. So, if 3 marks on a bolt head, it would be a grade 5 bolt, etc.
• Make sure a bolt goes - at absolute minimum - all the way through its nut, or a few threads more - when assembled.
• It is recommended to use Grade 8 or "AN" bolts on suspension and driveline components for maximum reliability and safety. Also con skier stainless iiirdwalic for use on your car because it "does NOT RUST"!
OTHER RELATED ITEMS
Nuts: Come in various types. Plain, nylon-lock, jam nuts, castle nuts, etc. Recommend nylon stop nuts as the best general-purpose use.
Cotter Pins: NEVER-EVER RE-USE a cotter pin! When using a cotter pin to lock a nut, bend one end of the pin over the top of the nut, and the other end down and  trim it if you have to. This provides maximum holding strength.
Washers: Split washers like used on our MGs - are practically useless for keeping nuts from loosening up (but they might help prevent "galling" when tightening). Consider other type washers like "Star Washers'', or using a thread locking compound like "Lock-Tite" - a liquid which acts like a glue between the nut and bolt.
Safety Wiring: Not as simple as you might think. Get info on how to do it properly if you decide to do your own.
Tightening: Wherever possible "Torque" nuts and bolts to proper specified amounts. This will provide proper clamping force while preventing over-stressing, - which might cause failure. An excellent resource all about automotive hardware is Carroll Smith's hook "Nuts, Bolts, Fasteners, and Plumbing Handbook'

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