Bathroom Window Balancer - Small

Thanks for posting. Is the metal channel 12" long, not including the nylon attachments at both ends? If so, this looks like either an S390-12 or S351-12. The only difference between these two balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement. See the diagram below for reference. Measure your old balance's shoe depth to see what matches best.

Comparison of the S351 and S390 balance shoes.

You then have to choose a stamp option, which reflects the balance's strength. If there is no stamp on the old balance to go off of, weigh the window sash these balances support. You can use that exact weight to choose the right stamp option. Let me know if you have further questions.

Yes, as I said, the length is determined just by the metal, not including the nylon attachments. Therefore this is either an S351-12 or S390-12, the difference being the shoe depth as described above. Let me know if you have further questions. 

An 11-1 stamp would suggest that 1110 is the right stamp option. That stamp option designates a balance that can support a window sash in the weight range of 3 through 6 pounds. If you want to be safe, weigh the window sash to see if it falls in that weight range. Let me know if you have further questions.