I have a 2019 Imagine 2500RL and need to repair some of the shades that have fraying strings. I called GD customer service and was told they did not know the string size. They gave me a part number for one of the shades and told me to contact Irvine Shade & Door. I tried calling and got no answer. I have sent an email, but figured this was the best place to get an answer. I understand I could ball park it, but when I go to the website fixmyblinds.com and see that many of the diameters are only 1/10 mm in difference, I start to believe that having the exact diameter might be important for proper function. Thanks for any help.