Screw used to secure spiral counterbalance to top of window frame?

Hi. Subject says it all -- the proper spiral balances arrived after order, but I'm clueless what screw to use to
secure it to the window frame. (Original screw appears lost to the ages.) If you can give me the proper specifications, I can go to the local hardware store and get some. Thanks. -Gary

I think that's probably it, although I might source a slightly longer screw. At 1" there may not be enough screw coming out the other side to grab and hold securely. The important thing, of course, was the screw diameter. Thanks!