Looking at Normandy Fasteners’ web-site I see they offer what I had always known as “hank bushes” – the hexagonal bushes fitted from the rear of the panel by expanding the shank, itself countersunk like a union nut, into a countersink on the outer face.
Once installed, and especially after painting, they are indistinguishable from plain nuts and I can think of many uses in model-engineering, so I am surprised our suppliers seem never to have heard of them.