As memory serves me, and without pawing through a bin full of old grease guns, what you have there is a high pressure gun with a swivel accessory and a changeable tip accessory. Both were quite expensive back in the 50s.
The changeable tip collar is not a grease fitting engaging tool, different diameter than the brass fitting with steel retaining pins for the nozzle. It should only index to the male tip on the back of your zerk tip. That seems to have been done to prevent the greaser from attempting to crowbar brass fittings with the gun. Given that you have 2 accessories the gun might also have the fitting to engage the refiller mounted on a 20 gal drum.
Before hydraulic hoses there were flex steel "hoses" similar in design to the plastic popit bead coolant lines used on machine tools. Solid pipes even with swivels could only get the head into so many tight spots.
BTW, the changeable tip gun generally came with a sheetmetal carrier that had sockets to hold either 4 or 6 tip assemblys.
The kit became very unpopular along with the guy who bought it rapidly when it was realized it allowed greasers (often not the smartest workers) to grease everything they passed on the line with the same grease.
You haven't enjoyed life till you have the joy of a 10hp 3Ø motor with a couple pounds of grease in each bearing area. I've been on many jobs whert all the motors had 1/8 pipe plugs in place of the grease fittings.
