First 2 sets are for anti-clock drive mags.
3rd set is for a clockwise drive one - so is good for Vincents (singles or twins), some early Oilfield twins, some other rarer older machines - and any number of 4 cyl mags for cars.
Of course, ones for 'Vincents' are worth more as a matter of principle - and in fact they may actually be, if they have platinum points, which are worth a few £$€.
Brass backplates are all handed according to rotation, and so are BTH and Bosch and most others - but the later steel backplate Lucas type can go either way if there is a contact on the second 'wing' of the fixed point carrier. Most replica sets don't have 2, all Lucas originals did. But the opening point can be fitted either way up / round. A drawback with the later type is that they can't take an auxiliary earth brush - and for older Lucas mags with no earth bar a brush on the back of the cb unit, 'tis a problem.
At the moment, new parts are getting harder and harder and we should all - I mean this seriously - hang on to any contact breaker parts, even well-knackered ones. It's always possible to graft new tungsten tits on, and worn pivot posts and oval holes in the spring point can be sorted if they really have to be.
The supply of replica steel ones has dried up - although the rights and the tooling are now in the hands of Grove Classics apparently. Nothing has been forthcoming for several months afaik.
It is worth bearing in mind, though, that most cb backplates have standard dimensions. Which means that in cases of despair, a BTH or Bosch unit (or various others come to that) can serve. It may - probably will - mean having to 'adjust' the position of the integral keyway on the male taper to get the points to open at the correct time relative to the armature/magnet position, but there are some advantages to the design of, particularly, BTH parts compared to Lucas.
Adventurous folk may want to have a crack at making their own backplates . . . all I can say, having made a few (and not very satisfactorily), is I found it darn hard and not a good use of time. However, people with better skills and tooling more suited to repetition work than mine could actually make a useful contribution to their beer funds I reckon, looking at what tired units sell for on e-bay. New proper quality cb units complete, for face cam mags like N1 and magdynos, go for around £75 - no reason why 'ours' aren't worth similar, if there's quality . . .
