Window clip

You can never trust a measurement that's read from a tape measure in a photo, unfortunately. There are too many factors that interfere. Take a look at the 18-196 sash guide pair to see if it matches your dimensions. If it doesn't, then type out the dimensions of the part for us, so we know how it differs.

Hmm... to be honest, I think you'll be fine. I don't think a 1/16" less on the top cap width would hurt in the operation of the window.