Mastic channel balance.
A quick learner from Wenonah, NJ says:
April 25, 2016
I order the part for mastic window, the channel part, S670-21 but when i put it in the wondow just closes, its too loose. It wont stay open
Tom from SWISCO responded:
April 26, 2016
It sounds like you didn't charge it when you installed it. Spiral balances like our Series 670 have to be wound up a few times during installation so that it acquires the proper tension. You can use a tool like our 75-006. See the guide below for further instruction.