This is a set comprising a sliding puller and a tear-shaped cord end to suit a small canvas backpack, like these that kids carry house shoes to kindergarten in.
These fit a 6mm diameter cord (should fit 1/4" cord too, for imperial-sized cords). Can be scaled to suit thicker cord, I don't think it'd work under 4mm though
Split STL and print the way up they are designed. The tear-shaped cord end screws together. The slider cap is press-fit and cannot really be disassembled after putting together, so put the cap in only after putting the cord in and tying a good knot at the end.
Made for my little one to fit a backpack she got from her grandma. Rough dimensions for a backpack are provided (note, these are not for an adult, but for a kid about 90cm / 3ft tall).
See photos for details.