Window balance replcement

Thanks for writing in. This looks like either an S380-27 or S385-27. The only difference between these two balances is the depth of the bottom nylon shoe, so compare both with your old hardware to see what matches best. The diagram below shows the difference. For the stamp, 26DS33, that 33 should indicate you have a 33 pound window sash, in which case the stamp option of 2660 should work for you--this supports a sash in the weight range of 30 through 33 pounds. You can weigh your sash if you wish to be certain. Let me know if you have any further questions. 

Comparison of the S380 and S385 balance shoes.