Hello Jason, and thank you for your inquiry regarding this item from Prime-Line Products. Yes, it does matter which item you purchase... you'll want to measure the width of the channel if possible, or the width of the backing from the old weather-stripping, and purchase the weather-strip whose dimensions match best. The difference between model numbers T-8658 & T-8659 include the following: Model number T-8658 has a 1/4 in. wide backing with .160 (5/32 in.) tall fibers, while model number T-8659 has a 3/16 in. wide backing with .156 (also 5/32 in.) tall fibers.
For additional questions regarding this item, or any other product manufactured by Prime-Line Products, please call their toll free number at (877) 649-9740, or contact them by email at firstname.lastname@example.org