Thanks for others commenting they had to file the corners to get it to fit. I was prepared, so a little filing until it would slide in and works perfectly. My faucet is from 1986, so I suspect some slight variation over the years in sizes? Anyway no more leakage!

I had to order a replacement part for my 20 yr old outdoor faucet and they had it and shipped it right away. A plumber wanted to charge me $300 to "repair" it and I saved $225! Thanks for your fabulous service.