I would like the hive mind on this one.

What QD device would a Rotex 556 X need to go on a SIG 553?

Hoping you folks would know easily.

Thanks as always.

Well, it's made for NATO-spec A2 hiders; so, that.

In messing with various A2-attachable silencers, I have discovered that some are more accommodating (and flexible) than others. Much of the flexibility depends on the depth of the silencer's mounting pocket. I have never fiddled with, or even held, a Rotex-X. You potentially have open and closed tine options of various lengths. It seems that the Rotex-X requires a flat portion, for the gate to index with. A device that is otherwise compatible, but lacks a flat spot in the right spot, can potentially be made compatible by having a 'smith mill a flat in the appropriate place.

There are a lot of options for A2-compatible cans. This is all assuming your 553 is 1/2x28, and not the LH thread seen on some.

Another thing to keep in mind is the very small shoulder on the 553. It can prove problematic, when it comes to timing certain devices.