due ruote 

Well, the title pretty much says it all.
I am using a Stronglight 93 crankset for a single speed conversion on an old Stella. The crankset was previously used with a JIS spindle, and bottoms out now on the Stronglight cup and cone spindle that I have. So it would seem that throwing in a VO unit, which uses a JIS taper, will be the simplest fix. My question is which length? They come in 103, 107, 110, 113, 116, 118, 122. TIA

3alarmer 

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...if by bottoming out, you mean that the crank socket is hitting the end of your Stronglight spindle when you tighten the bolt, I would not presume another JIS taper will fix your problem. If you have a JIS spindle or BB unit lying around (in any length), I would dry fit that to the crank arms first, to check, before I spent money on a VO unit.

Then I would probably just measure the Stronglight spindle and order something pretty close. You can adjust the chain line a little bit on a single speed application by chain ring placement, if you have to.

You can go a little short, because you don't need to worry about clearance for the inner ring/chainstay as much, with your (presumably) smaller, single speed chainring.

Dry install what you have, with the French thread cups and spindle, and do some measuring of how far out the crank sits when it bottoms out, and your clearance for the ring. Then figure the JIS spindle will probably move it out a couple of mm's. There's probably someone here who knows an exact formula for this, but I just dry fit stuff like this until I get something that looks good to me.

due ruote 

@3alarmer, thanks, that’s pretty much how I have gone about it in the past. I can probably figure it out that way, but with an asymmetrical spindle and a symmetrical cartridge, I was sort of hoping someone had already gone down this road and had the answer.
I did dry fit the crank on a JIS spindle I have laying around and it looks fine. The issue is that the Stronglight spindle isn’t JIS. Unfortunately I must have thin cups, so the distance between the races doesn’t match between the two spindles. If it did, I would just try swapping in the JIS spindle.

JohnDThompson 

Stronglight spec'ed a 113mm spindle for their track cranks:

due ruote 

Thanks. That’s helpful. Around there was what I was expecting.
Edit: So here's where my thinking is presently:
I stuck the (assymetrical) Stronglight spindle in the fixed cup (stilll in the frame) with the short end on D/S. In this configuration the crankset is in a good position, with a few mm clearance between the chainring and stay. From the BB shell to the end of the spindle it's 23mm. For a symmetrical BB, double that and add to the 68mm shell, and I get 114mm. So that more or less matches the 113 suggested above. However, 113 was spec'd for a pista crank, whereas I am using the outer spot on a double, which I am guessing (though I'm not positive) will put my ring a bit more outboard than a pista. Also, although the crankarms have apparently deformed slightly in the direction of a JIS taper, I still expect they will sit a bit further out. Hence, I am leaning toward ordering a 110mm BB, and using a shim on the driveside if necessary.
Does that make sense?