Unknown windows need parts

Thanks for writing in. This looks like a Series 751 channel balance. You'll need to remove the balance from the window to confirm it matches the specifications on the product page. Confirm the length of the metal channel--this should be 24", in which case you'd need the S751-24, with a stamp option fo 23B; but let us know if it differs. For your tilt latch, compare the dimensions to our 26-188W.