I have a 3350de BSI. the length is 34" but i am having a hard time picking between the 390 and the 351 for my window. its a half inch width too.
Anthoni
Tom from SWISCO responded:
June 13, 2016
Thanks for posting. The only difference between these two balances is the depth of the shoe. You will need to measure yours to determine the better match between them.