Hi Howard,
I bought one of these, following an advert in the Vintage Motor Cycle Club of Victoria (Australia) magazine in the early 1980s. From memory, the place was out on Sydney Rd, Melbourne (maybe around Coburg), and there was a VERY large box of them! Sorry this doesn't help much with the question; perhaps they were for some kind of industrial application? That said, a press down spring-loaded plunger is a pretty labour-intensive device compared with a gravity feed. Because the fitting on the bottom is larger than the hole in the top mounting plate, a question arises about how the thing is assembled into the oil tank.
Leon