This is the last design of Activator mounted dispensers and they only fit on the narrow posts of the last years of Filter-Flo's, both regular and large capacity machines.

There are still a lot of these around; the good news is that these later ones work better than the "Jet Swirls" that came in dealer boxes with sample-sized bottles of Downy and Sta-Puf. According to Consumer Reports, their early dispensers never fully dropped their loads in the final rinse; they said they'd spray out the remainder of the liquid softener during the final spin "where it did little good".

I'd put in on eBay for a starting price of 5.99 and set the shipping and handling charges to make it worth your trouble and time. I have about 5 of these and should be selling them on eBay but it's so far down on the list I know I won't get to it until I'm 80.