The Redrock Micro Cold Shoe Mounting Spud can be used in two ways to attach a cold shoe mount accessory, like a camera monitor, to a rig or a piece of equipment.

With its rod-like portion 15mm in diameter, the spud inserts into a 15mm grip opening of something like Redrock's microMount or Grip Rod, just like a 15mm rod inserts into and gets tightened in such an opening. That's one way. The other is by screwing the spud onto a 1/4"-20 screw. Underneath the rod-like portion is a 1/4"-20 screw-hole for just that.

Either way, once the spud is attached on something, you can mount various cold shoe accessories on it.