We have them in almost every window in our house. Each one is custom sized because the windows were built on site when the house was.
They make a big difference in draft control. My only problems with them are 1) where to store the ones we take out in the summer so we can open windows. I'm working on planning better storage. 2) They need to be carefully labeled since, in our case, they are not interchangeable. 3) the windowsills are now too narrow to put anything on. Tho maybe that's not such a bad thing. Empty windowsills look neater.
Kathy

What brand are yours?

You are the target market for this relatively-obscure product:

Here is a link that might be useful: Acro Storm Window Numbering Tacks

Oh, shades of yesteryear!! My folks had those on their storm windows and screens! I hadn't thought about them for 50 years or more! Now to get some genuine storm windows so I will need those numbers!

Innerglass in Connecticut. We live in NH. We picked up the first one at their shop and liked it, then they delivered the next 30. My dh had to carefully measure each window. They gave instructions.
I remember those numbers too. Thanks for the link, I'm not sure they will work unfortunately because these have plastic frames with spring expansion.
Kathy

Here is a link that might be useful: Innerglass

I've seen those windows somewhere. On TV? Worth a serious look, that's for sure. Thanks.