As Almost Trick says, length is important. The sleeve (nut) cannot be too long! If it is, you cannot fully tighten the bolt, there will be a little looseness and you will quickly elongate the spider holes and kill the crankset. With a single bolt set you will be fine. (And longer sleeves can be filed down. General rule: put in the sleeve, no bolt. Pushed in solidly, it should be short of the outer face of the outside chainring so no matter how tight you tighten the bolt head, the bolt (or its washer) never contacts the sleeve. The sleeve just needs to be long enough to get (say a mm) past the inside of the chainring.