I'd use M6, IME they fit well enough for light duty. You are only locating a light loudspeaker on a frame. If it were a car's suspension, no. But a speaker? Go on then.Thanks again all - so you reckon 1/4 BSF Steve? I'll probably order a small quantity of a few just in case.
Please remember - I left England in 1995 never to return...I have been living in mostly metric lands every since, and find all these thread pitch differences as confusing (and frankly, unnecessary!) as hell
2.54. Exactly.OK, thanks - I actually have some calipers. Remind me again...how many cms in an inch?
2.54. Exactly.
It wasn't really, but the metre is now defined as so many million light wavelengths and the foot was never so defined, so it was set to 25.4 mms precisely because that was what it measured and it made the maths tolerable.
As for not having inches in Switzerland, what size are TV screens there, and car tyres?
I understant zat even ze Tchermans still use inches ven specifying the size of water pipe fittings. I thought they were supposed to be engineers.Thanks...and f*ck off Actually, TVs now have both inches amd cms in their Ads...but wheel diameter & width still exclusively inches...while offset is in cms Even that confuses the hell out of me!
BA threads are intriguing, they use all imperial measurements but the thread pitch is metric. This was something invented in, when, the 50s?
Thinking about it, of course it predates the 50s. It was at its heyday then. I hadn't realised though that it was *intended* to take over from BSW and BSF in the small sizes. I didn't know it was *entirely* metric either. How odd.BA
Bit before that in fact - 1884. It is actually an entirely metric based thread scaled from 0BA being 6mm major diameter by 1mm pitch though the dimensions are normally shown as imperial.
https://en.wikipedia.org/wiki/British_Association_screw_threads
In our hobby, BA is likely important, since it was/is used a lot for electrical connectors (and until VERY recently was the thread of the screws holding the cover plates of wall switches and sockets in place).Thinking about it, of course it predates the 50s. It was at its heyday then. I hadn't realised though that it was *intended* to take over from BSW and BSF in the small sizes. I didn't know it was *entirely* metric either. How odd.
until VERY recently was the thread of the screws holding the cover plates of wall switches and sockets in place)
I didn't know it was *entirely* metric either. How odd
The [BA] threads are also linked to the number scale drills, although I have always assumed that the UK version is not the same as the US.
How are the BA threads linked to number scale drills?
That means (only) that number drills are finely gradated enough that there exists a number drill that is near enough to fit the spec, which is certainly true.LOL, far too long ago, but the engineers in the tool room would always shout a number whenever we asked for the tapping drill for ?BA (usually 2 or 4). I would assume that logic would be right and that The BA defined a number and letter twist drill "set" that correlated to threads.
The screws holding my Britool ratchet together are 3BA. I had quite a task finding a replacement, since one of them was missing...I don`t think there is a direct connection between number drillls (I only know and use the British number and letter drills).
It is a convenient feature of BA threads that the tapping drill for most sizes is also the clearance drill for two sizes smaller, i.e. tapping size for 4BA, number 33 is clearance for 6BA.
Mostly only even BA sizes are used, I only once have found a 3BA thread, on the pendulum of a Victorian clock.
That means (only) that number drills are finely gradated enough that there exists a number drill that is near enough to fit the spec, which is certainly true.
(My 1976 Zeus table only gives drill sizes for BA tap and clearance in metric and decimal inches)
BugBear
How do you work that one out?
In a workshop with imperial, metric, number and letter drills, it just happend to be the number drills that were a best fit to BA tapping drill requirements.
What you are effectively saying is that there are no drills at tapping sizes for BA threads, just lucky happenstance that number drills do the job.
There is a BS recommended tapping size which gives a particular percentage of thread depth, it is common to adjust this figure according to the material and thickness to be tapped. thus two or three different adjacent number drills could be the appropriate tapping size for a given application.