Window Balance 21 12 BS1 R

Thank you for your interest in SWISCO hardware. It looks like you either need the Series 351 or the Series 390 channel balance. The difference between the series 351 and series 390 balances lies in the shoe. The series 351 channel balance has the 15-002 shoe while the series 390 channel balance has the 15-001 shoe. The 15-001 shoe is 1 1/8" from front to back. The 15-002 is 1" from front to back.

It's impossible to determine your stamp option with this number. You are going to have to weigh your sash.