If it's a SIG 556, it uses STANAG (AR-15) type mags
I figured as much but when he said clips that hold them together, for some reason I read that as little nubs like the 550 mags.
I knew they had made a run of Sig 556 rifles with 550 lowers. Thought that might have been what he was talking about.
I didn't realize the Sig 556 magazines clipped together.
I generally try to avoid Sig 556 anything.