I have a spare, old water circulating pump, a Grundfos 15-50, like this:
https://www.anchorpumps.com/media/catalog/product/cache/adc97c95711116b76690f2d96fb29368/l/e/leoldshite_1.jpg
About that silver screw in the middle, can it be obtained separately? It's missing from the old 'parts' pump.