This is the SWISCO Series 351 Side-load Channel Balance Sash Support System (also known as a block and tackle balance) for non-tilt windows. The series is determined by the combination of the top and bottom fittings attached to the metal channel.
When determining length, only measure the metal channel; do not include the fittings in this measurement.
The metal channel's width is 9/16", but is considered 1/2" in the trade. It houses a spring and pulley system to raise and lower the sash and comes fully assembled with a non-winged 19-002 top guide and a non-winged 15-002 (1" deep) bottom shoe.
Please note that the Series 351 closely resembles the Series 390 channel balance, but they are not the same. The difference lies in the depth of the shoe: unlike the Series 351, The Series 390 balance has a 15-001 (1-1/8" deep) bottom shoe.
