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Metric/Imperial Threads

vibrac

Well Known and Active Website User
VOC Member
If you are really interested in weight saving what we really need are aluminum high strength imperial nuts 1/4",5/16".3/8".1/2"
 

Magnetoman

Well Known and Active Website User
VOC Member
Oriental metric threads are standard as in Europe
That's true now, but it isn't true for bikes made before the mid-1960s. Prior to unifying under the ISO banner, each country had its own version of metric, including the Japanese JIS. Although in most cases the diameters, pitches, and A/F head sizes were the same, there were some notable differences to catch the unwary. Also add to the list the German Löwenherz, which are metric fasteners but with 53° 8′ pitch angle and commonly used in places where the British used BA. Bosch magnetos through at least the 1920s used Löwenherz fasteners.
 

Vincent Brake

Well Known and Active Website User
VOC Member
Oh, and then theres PanzerGewinde, PG.
80 degrees. Latley mostly used on Electrical ferrules.

And B32 collets on a Schaublin have tooth like a sawblade. pulling angle 5 degr, other angle at 45 degr. Outer diameter 29.7 x1.693 mm pitch.

So the odd threads... Are going on...
 

oexing

Well Known and Active Website User
VOC Member
Never heared about Löwenherz fasteners, and I got a BMW from 1928 with Bosch Magdyno. Certainly they had some M 4,5mm and 5,5 mm screws, M 3.5mm electrical norm screws, but these are common 60 degrees profile. BMW at that time had M 6x0.85 screws , a pitch that nobody else used. Well, that was long before some standardisation seemed a necessity. Not so rare are M 7 x1 screws and bolts, used on Horexes, Citroen, Russian aircraft, and lots other types , still easy to identify without mysterious files to look up .
We don´t need to speak about special segments of trade like round thread electric household bulb sockets, yes, Deckel mills had collets with S20x2 mm saw tooth thread profile, not to mention a myriad of weight and length names.
Another weird way of defining head hexagons is wanting a spanner for a BSW bolt 5/8 or so, you cannot tell from that type what size the hex head is across flats. Got a different screw with unknown thread, so what spanner will you hunt in your garage for this case ?? So get out a vernier and take the size. Then look up a file to compare that size to any norm that happens to have same spanner ? No wonder anybody in imperial world is seen carrying a monkey wrench around 24 hours a day , hopeless to know what he is going to need for next bolt. A real mess , even without having metric fasteners in your garage. My suspicion is tradesmen had in their mind a wish to discourage Joe Public from tackling any job the tradesmen wanted for themselves and to show off their "impressive trade skills" . Or why would one want to grade wire sizes, drills, small screws, electric wires in numbers and not by real measurable sizes in inch or millimeters for checking what you got before you ? And that with smaller size at higher numbers - what sick brain has come up with this logic ?? It is just right that only 5 percent of world population still remain in this obsolete age . . . . .

Vic
 

Magnetoman

Well Known and Active Website User
VOC Member
Never heared about Löwenherz fasteners, and I got a BMW from 1928 with Bosch Magdyno. Certainly they had some M 4,5mm and 5,5 mm screws, M 3.5mm electrical norm screws, but these are common 60 degrees profile.
Are you sure about that? Did you actually measure the profile with a microscope or comparator? It's actually pretty difficult to do with reasonable certainty with screws that small, and if you assumed that since it's metric it had 60 degrees it would have been very easy to think you saw 60 degrees.
And that with smaller size at higher numbers - what sick brain has come up with this logic ??
It actually makes a lot of sense. Once the smooth progression of, say, drill bit sizes was decided on, having a machinist ask the tool room to give him a #47 bit is a lot less prone to error than asking for a "zero point zero seven eight five inch" bit.

As for BA fasteners, it makes excellent sense to have them in a geometric progression so it makes sense to number them by the power they're raised to rather than either some arbitrary number or their measured pitch. Since pitch = 1mm × 0.9^n the larger the BA number, the smaller the pitch. So, you devise a system where the machinist asks for a BA4, or asks for one with "thirty eight point four eight" tpi.
 

Magnetoman

Well Known and Active Website User
VOC Member
Never heared about Löwenherz fasteners,
Gentlemen, what no mention of 'letter drills'?
Despite living in Germany, the German Löwenherz thread system came as a surprise to oexing, so I hesitate to think how he will react when he learns about the ß, ö and Ö letter drills, to name just a few (the Ö drill bit, of course, being 0.001" larger than the ö).
 

vibrac

Well Known and Active Website User
VOC Member
Of course the whole thing is blured now most of the time on a metric lathe I need a imperial dimension. So I open it to the imperial measure I want then zero the gauge switch to metric. then measure what I need to take off and measure and cut till I get to zero. I keep promising to fit a DRO system to my Harrison but I am quite happy....
I have two draws for my spanners "Open" and "Ring" I keep promising myself to buy a set of Metrinch but I am quite happy....
 

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