I have 20 year old Mercer vinyl windows that one of the spring lifts cords broke. Images are attached. Total length is 28 inches. The markings are in the third image provided.
Tom from SWISCO responded:
October 12, 2018
Hello! Measure your bottom shoe. If you have the 1" shoe below, choose S380-27 (2640). If it's 1-3/32" or so, choose S385-27 (2640).