The standoffs don't normally interchange between an XM-18, and the larger XM-24. The XM-24 has a thicker blade than MOST XM-18's. The blade in an XM-24 is 0.185 inch thick. The blade in MOST XM-18's is 0.165 inch. So the standoffs are a different length, by 0.020 inch. That is a lot in the world of precision machinery. Knives are extremely precise little machines.
But there is an exception: the FATTIE Hinderer XM-18 have a thicker blade. The blade in a Fattie XM-18 is the same thickness as the blade in an XM-24: 0.185 inch thick. So the standoffs made for a Fattie XM-18 SHOULD interchange with the standoffs made for an XM-24. And vice versa. In theory.
I believe I am correct about this. If I am in error, I apologize. I just don't want people getting parts that won't work for them. This should be pretty easy to verify. Or disprove. Better to get this figured out, to prevent future difficulties. I have no interest in this except wanting to help.