What size and replacement do I need to order

Thanks for posting. This looks like either an S380-30 or S385-30 Channel Balance. The only difference between these two balances is the 'depth' of the bottom nylon shoe, or the heel-to-toe measurement. See below. Measure your old balance's shoe to see what matches best. In either case for a stamp option go with 2920.

Comparison of the S378, S380 and S385 balance shoes.

If the shoe is worn from use, then there is a good chance it was once 1" in depth when it was brand new. It happens all the time.

In a worst case scenario, should the shoe prove to be too deep for your window, you can always trim it down to size with a utility knife. Just make sure to wear safety gloves if you try that, just to be safe. Please also note that any product altered in that way cannot be returned for a refund.

I'm sorry to hear you're having trouble. I'm not sure why that might be happening, though. What you've described isn't a common issue. 

Can you go into more detail? How exactly is the window getting stuck? Are there any damaged components, either on the window or balance? Are you making sure to hook the balance into the right hole?

There are honestly a TON of reasons why a balance might jam a window on accident, so it's hard to pin down without more information. If you haven't already, make sure to watch our video on how these balances are properly installed.