Means like the ones I post above.....Alu? No matter what type of Alu, I doubt it'll be as strong as steel. But I guess the pressure on the spacers won't be significant enough to bend or dent the alu. I've seen worn out alu crank pulleys before and it's not a pretty sight!
It's probably those spacers that come with the studs. Rare stuff and pretty downright awesome if done right