This is a drawstring brake/clasp used to easily adjust the drawstrings on gym shorts, backpacks, or anything else that your heart desires. 

I have had success printing with ABS, 0.2mm layers. PLA warped in the washer/dryer, but the ABS is holding up just fine. I would recommend printing the slide with 100% infill since my first few iterations with less than 100% infill tended to break at the smallest diameter.