As original to a Cobra or 427 Cobra sent to America, not that I can see in that picture.
The old thread in the AC Owner's Club site has been lost in a website incident but I created a album in this forum to put some of my images in.
AC Cars supplied grease guns - Club Cobra Photo Gallery
Also because there are multiple taper tip adapters I will add an extra comment on nozzle tips. The ones I expect for USA Cobras and 427 Cobras utilize the small diameter cone that cups grease fittings with a taper at the end with a circumferential groove cut around the straight section near the taper. (There is a similar tip without the groove.)
I have examined, have, or have had ones with
• two different length body cylinders
• three different closed ends, two different pleated versions and a round cap design
• several different adapter tips, some tips could be ones owners swapped in somewhere along
• two different "GB 2800" embossed caps, i.e. both marked GB 2800 but they are embossed with two different patent numbers
• different colors/type of pain on the cylinder bodies depending on body design