Universal M-12 freshwater cooling pump questions

[michigander]

I am replacing the cooling water">engine cooling water pump on my Universal M-12. Found the Oberdorfer replacement N202M15 and 16. They list the differences as the port measurements being 3/8” and 1/2”. I measured the inner diameter of the fittings that go into my current Sherwood pump and it is 1/2”. When I called to order the Oberdorfer they had the 202M16 but not the 15. The 15 was specifically listed to fit the Universal M12 where the 16 was not specifically. Rep told me they both should work and as my inner dimensions of the insert fittings are 1/2” I ordered and received the 202-M16. Received today and now I am questioning if it will work. The inner dimensions of the in/out coming off the actual pump are 3/4” ? Probably a stupid question but why do the actual pump specs call it 1/2” ports?
Anyone with any experience with this able to give me some help? When I look at the blow up specs for both pumps all the component parts are the same except the pump body. I’ve found another vendor that has the 15 in stock if the 16 won’t work. Any help would be greatly appreciated, thanks!
Roger

[Ballsnall]

Pipe threads are measured by the bore size not the thread size, I blame the British for that.

[Nord Sal]

Yes. It'll work fine, it's the same pump but with different port sizes. You'll just need to use different hose barbs to fit the 1/2" ports or use your existing hose barbs and 3/8 x 1/2" reducing bushings.