Will this fit eureka power plus 12 amp max pro?

I don't know for sure. If the model number is somewhere on the vacuum, you can use the link in the listing to check whether or not these belts fit. That's what I did before I ordered them for a 12 amp mega boss - big, old heavy Eureka Victory upright. Another thought. The listing says fits all Eureka Victory uprights. If your vacuum does not have "Victory" in its name, then maybe so, maybe not. Hope that helps.

We have an older eureka victory upright model 4325 serial #09812052558 and can't find a belt to fit. which one should fit?

I don't the use my old Eureka Victory Mega Boss (no clue as model number) but as I recall these did work for it. Ha! Just looked at my review. These did fit my Eureka Victory Mega Boss (new around the year 2000). They are advertised as fitting any Eureka Victory upright. Also Eureka brand size U belt package states it fits models 4100-4600. https://www.amazon.com/Eureka-Style-U-Belts-61120/dp/B008MKNG6U/ref=sr_1_2?crid=1RVB6DD029PB4&keywords=eureka+uu+belt&qid=1668281750&s=home-garden&sprefix=eureka+u+belt%2Cgarden%2C156&sr=1-2