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I have a double and a triple chainset going spare. Which would be best to use for a 1x10 set up?
Whichever one has 104mm BCD. If that's both, then whichever looks nicest. If that's neither then by a third with 104mm BCD.
And get a chain device (conincidentally I have one for sale....)
You'll likely get a subtly different chainline using a double or triple (and depending which mounting position you use on the triple). However, I doubt you'll notice the difference in practice so use the one you like the most.
some doubles (SLX) won't fit a NW ring due to the spider getting in the way. I run a SLX triple with a RF NW 32t ring on the middle position and it works a treat.
The triple - chain line will be better.