Seatback bag / cargo hooks

thingiverse

Two friends with young children were impressed by my previous design for a pram cup holder and found the pram cargo hooks an excellent idea, but they needed them most in their car. I discovered a great seat-back hanger that utilized the headrest rods as anchors, but it used d-clips that made noise for the babies and were too awkward to use when hanging a nappy bag during a long car trip. So, I combined the best features of both designs. The design consists of two parts to ensure layer lines run with, not across, the lines of highest load, making them stronger this way. It also allows for easy replacement of the part most likely to fail over time - the hook - and uses a more springy material like PLA+ or PETG for the main body. Ideally, keep the hook made from PLA or ABS so it can handle heavy shopping bags or full nappy sacks without bending. The two parts are tightly connected and require some force to seat together - make sure screw holes align well before joining with M5 16mm machine screws (pan or button head). A lot of torque is needed, but the thread will form its own path. It doesn't need a nut as the thread is tight enough to prevent the screw from backing off, and it only holds the parts together - the flats of the parts prevent the hook from rotating. My prototype had a nut, but it added complexity and expense without providing clear strength gains. The arm's length was designed for Skoda and VW seats, but it should fit most modern car seats with removable headrests. The holes are slightly under 14mm, a snug fit that can be drilled out more if needed when printing with four or more walls. I added a curved not straight gusset to the hook to avoid leaving a dent in the seat piping.