I bought this last weekend in rusty condition and minus blade. According to the 1938 William Marples catalogue it is a leather washer cutter. I have cleaned it up and made a blade. Now I just need to find a use for it
I'd say you are now very well placed to start buying the sort of splendid old brass footpumps that Rhyolith likes. When you find one with old leather washers that are cracked and useless, you'll be ready!
Also ideal if you rely on an old cast iron pump for your water supply...