Fixings - Metric vs Imperial

[Parazine]

Don't disagree Roger but the whole UNF/UNC venture seems like a wrong turn with hindsight. Funny how each successive attempt at standardisation has merely resulted in another layer of confusion.

It was a huge "wrong turn". To switch the whole of British industry over from BSF/Whit to UNF/UNC in 1948-53 and then again to metric in 1968-73 must have cost millions.

Political short sightedness!

[Bob Culver]

I guess the cost was largely in damage due mix ups. Production taps and dies short lived anyway.
The crusty old Pom father of a school mate used to maintain the only advantge of UNF was nuts easily split with a chisel.
In undamaged precison form the UNF is relatively strong but easily damged. Millions of US cars and planes not entirely wrong. (There are detail differences ANF,ANC, SAE and UNF,UNC). Whitworth remained for much general hardware. I bought a good tap and die set around 1970 and it was UNF/Whit. The later practice of UNF heads on BSF was irksome.
Turning the heads unfortunately removes the strength indicators very useful when hunting through old for BSF .

[A G Wood]

*What really bugs me is to see modern bolt heads with raised letters. These should be machined off.*
This reminded me, of an instance 35 odd years ago when I used to deal professionally with an instrument repairer who had a side hobby restoring and exhibiting mostly early 1950s Triumph motorcycles. He told me he used to use UNF fastenings and rework the bolt heads to obscure their origin. Reckoned the judges never picked it up.

[andrew34ruby]

Recently completing my 1934 Ruby I took the view that it was far simpler, and cost effective, to stock up with metric fasteners and have a variety of diameters and lengths to hand. BSF and BSW were purchased when needed, for example screwing into castings and into captive nuts.

I don't much regret this approach and the car is now on the road.

If I could have my life over again I would have carefully listed the various sizes required and stocked up with BSF from the start.

And then there is my other Austin from 1955, mainly UNF and a few UNC.

[Hedd_Jones]

When I threw my chummy together, which started as a thoroughly and properly overhauled rolling chassis (inc all imperial fixings), and 7/8 knackered coachwork. I used metric fasteners throughout for fitting the coachwork. M6 & M8, penny washers and nuts. All ex Toolstation BZP for pennies. And I still have a bucket full left.

I didn't bugger any existing threads, used the correct stuff where neccassary, but if it was just a plain hole needing a 1/4 bolt it got a M6 and M8 for 5/16.

I proceeded to paint the car with some satin black from Wilkos and it still isn't wired. I spent the 200odd quid I saved in the pub.

[richard wyatt]

The manual for my MG Magnette ZA included the statement .."the threads on this vehicle are metric;however for the convenience of owners who may already have a set of spanners,the heads are imperial.." No wonder our car industry died-I wonder at the cost of this quixotic gesture. I rebuilt using metric ; however for my sevens I always use imperial to avoid subsequent confusion.If you buy in bulk the cost is insignificant in the greater order of things -just label the remainders and remember where you put them !

[Rogerfrench]

Don't disagree Roger but the whole UNF/UNC venture seems like a wrong turn with hindsight. Funny how each successive attempt at standardisation has merely resulted in another layer of confusion.

It was easier to get Britain to convert to UN than get USA to change to BS, I'm thinking! UN still very common over here, though it's almost unknown as UN,  most often called Standard or SAE.

[Chris Garner]

In 1919, when supplies of the White & Poppe engine fitted to the Morris Cowley dried up, Morris turned to Hotchkiss et Cie to supply. Based on the US Continental Red Seal engine, didn't the metric fastenings used have British hexagon heads?

[Erich]

As many know, I'm a bit of a rivet counter, maybe more than a bit. Once I learned the Imperial system(BA, BSC, WW, BSF, BSPT, BSPP etc.) it makes perfect sense. It may be a bit over engineered, but the idea of using different pitches for different materials and purposes is very well thought out. And, I appreciate that Whitworth form uses a radius on crowns and valleys and so lessens the possibility of stress fractures. That said, I have been known to use 1/4 20 UNC nuts with Whitworth screws on items that are not critical. However, for the most part, if it came in imperial, then it imperial it stays imperial. Introducing yet another thread would make my brain full.

Erich in Seattle

[bob46320]

From WIKIPEDIA, BA are metric dimensions (rounded) and then converted to Imperial and rounded again !! So are not quite Imperial if you are a "Rivet counter", again the BA thread angle is 47.5 degrees as opposed to the 55 degree Whitworth form and UNF, UNC and BSC being 60 degrees .
This all leads to confusion when for example a Whitworth nut is "forced" onto a Unified threaded bolt. I don't think that keeping to the old BSW/BSF threads is rivet counting, just a simpler life if you don't get into the habit of using any old bolt that comes to hand. Sure, BSF/BSW can't be bought at your high street outlets, but are widely available from many other suppliers.