"The Enfield inch" when an inch is not an inch!

[Bruce_in_Oz]

And then there is the "utterly Imperial" BA system.

Well, sort of.

It is almost a direct lift from the old Swiss "Thury" system used by yodelling clock-makers. Start with "0" BA. It has a pitch of, give or take a gnats knacker, 1mm, just like M6. The form and flank angle (47.5deg) are, of course, completely different.

"1" BA is simply "0" BA multiplied by 0.9 to give to the next smallest thread. This process repeats ad infinitum (ad nauseum?).

Hence the almost incomprehensible "numbers" attendant to BA threads. I have NEVER even attempted to cut one on a lathe; metric or otherwise. just keep a set of BA taps and dies in the toybox.

An example of the "almost" relationship is the rear-sight adjustment screws on the FAL (metric)/ L1A1 (BA); VERY similar in diameter AND pitch but not close enough.

In the process of "Imperializing" the FAL to arrive at the L1A1, screws of the nearest "industry-standard" appear to have been sought, be they BA, BSF or something different like a Unified number thread or somesuch.

Remember these were the days when Vauxhall (GM UK) built engines with bolts having UNC threads but Whitworth-sized heads. Detroit-designed motors meant to be worked on by UK mechanics with "UK standard" tools.

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[bob4wd]

And then there is the "utterly Imperial" BA system.

Well, sort of.

It is almost a direct lift from the old Swiss "Thury" system used by yodelling clock-makers. Start with "0" BA. It has a pitch of, give or take a gnats knacker, 1mm, just like M6. The form and flank angle (47.5deg) are, of course, completely different.

"1" BA is simply "0" BA multiplied by 0.9 to give to the next smallest thread. This process repeats ad infinitum (ad nauseum?).

Hence the almost incomprehensible "numbers" attendant to BA threads. I have NEVER even attempted to cut one on a lathe; metric or otherwise. just keep a set of BA taps and dies in the toybox.

An example of the "almost" relationship is the rear-sight adjustment screws on the FAL (metric)/ L1A1 (BA); VERY similar in diameter AND pitch but not close enough.

In the process of "Imperializing" the FAL to arrive at the L1A1, screws of the nearest "industry-standard" appear to have been sought, be they BA, BSF or something different like a Unified number thread or somesuch.

Remember these were the days when Vauxhall (GM UK) built engines with bolts having UNC threads but Whitworth-sized heads. Detroit-designed motors meant to be worked on by UK mechanics with "UK standard" tools.

So that's the reason! I had a Vauxhall in 1963 or thereabouts, always thought somebody had their head in a dark place when it was designed. Sounds reasonable, except that I'm in the States and standard tools here still didn't fit! But then, the whole car was weird.

[Bruce_in_Oz]

Vauxhalls! God help me: I had TWO of the things.

The first was a 1950 "Wyvern" with REAL leather upholstery, front doors that opened the wrong way, windows that simply pushed up and down, swing-out "wing" indicators in the door pillar, 525 x 16 tyres (NOT good in the wet) and a raging 12 horsepower up front. I got rid of it after "bits" (exhaust valves, gear linkages, etc. started "breaking" with monotonous regularity. Dropping the head of an exhaust valve whilst the pistons are in action is an interesting experience, to say the least. Fortunately, my late father, being a good mechanic, knew where there was a spare engine. Into his shed; delete dead engine, insert "working" one.

The Wyvern was off-loaded on a younger brother of an old school-mate and I then "graduated" to a Vauxhall "Viva" of "mid-60's" vintage, a "hand-me-down" from my older sister..

Oddly enough, IT, in turn, died as a result of an exhaust valve failure as well; only at considerably higher speed and in the middle of nowhere on the New England Tableland in New South Wales...in the middle of Winter....just as it was getting dark. That was spectacular; the displaced valve head lodged sideways into the top of the piston. This, of course, was whizzing up and down at high frequency. Piston kicks sideways in the cylinder, sleeve cracks, contents of cooling system dumped into the oil sump, great white cloud billowing out the back of rapidly and noisily de-cellerating vehicle. Exit one motor.

After a few months of riding my "dirt bike" (mud-digger" tyres are "interesting" on wet bitumen, and especially on painted road markings after any sort of rain), and public transport to get to work, I "graduated" to an XA Falcon utility, which led to another series of "interesting" motoring tales. And then there was the "re-purposed" Ford F-100 ambulance.........