Actually, this arrived at the end of March but I just inked it up this past weekend. It’s a copper Esterbrook J with a #9461 rigid fine nib.
It’s my second vintage pen and second Esterbrook. It’s a eBay purchase I added to my accumulation because I/m I sucker for copper or bronze and I could add another hard fine nib.
The paperwork (the pen came with the original box & literature) refers to the nib as “rigid, fine” but I’ve also seen it described as a “manifold” nib. It’s designed to be extra strong for uses such as carbon paper. I figure it will also last longer with a light writer or be suitable for a non-fountain pen user to try.