I have a SRAM X0 crank on my MTB, and I want to buy some Shimano XT chain rings from a mate. Will they fit? Or is the BCD, Spider shapre, bolt size etc incompatible.
All are 10 speed.
I don't think they will unfortunately. I'm sure the SRAM X0 crankset (below) is 80-120mm BCD on the 2x crankset. Do you know which model of X0 crankset it is that you have? The BCD may be stamped on the chainring, like the one pictured below. Shimano XT, with the exception of their latest M8000 series XT cranks, have a symmetric 64-104mm BCD.
If you're unsure of your crankset model, or it doesn't say on the chainrings, then measuring the BCD is fairly straight forward. Wolftooth Components explains how to do it very well here.
I hope this helps!