This is a Curtain Hook/clip for the aluminium rail which weathers over time with the sun and cracks very easily... I had loads to print. I am talking about the clip not the aluminium rail.
This design is based on a 70's/80's type clip in which you place the clip horizontally into the rail and then rotate the clip vertically which locks the clip in place.
Then you can hook the curtain clip which is connected to the curtain (which you can buy bags of for pennies) to the hook. Simple!
I have not found the clips in the UK stores and in any case I needed them now not when B&Q/Home Depot opened lol.
Hence the reason for getting a 3D printer... Good for, I need it now and cant be bothered to go to the hardware store.