Window sash pivot bar

It's tough to say for sure what you have while it's still installed, but this looks like it might be the old Certainteed brand pivot bar. They don't make this anymore, but they did develop the 26-175 to replace it. Despite the difference in style, it should replace the old version.

This is assuming that you do have the Certainteed pivot that I'm thinking of. If not, or if you aren't sure, I'd be happy to look over some photos of the original part removed from the window. That way I can find you a better alternative.