Seatback bag / cargo hooks

Two of my friends, with 2 young children, liked the pram cup holder I printed a while back & I found the pram cargo hooks which seemed a great idea. However the place they needed them most was in the car. I found a great seat-back hanger which used the headrest rods as anchors, but they used d-clips which were a bit noisy for the babies and too awkward to use to hang e.g. a nappy bag on when a sudden change was needed during a long car trip. So I combined the best bits of the 2 designs...

The design is in 2 parts so that the layer lines run with, not across, the lines of highest load, and so the parts are going to be strongest this way. It also allows for the part most likely to fail over time, the hook, to be replaced more quickly and cheaply. Further, it allows for the use of a more springy material like PLA+ or PETG for the main body. Though ideally keep the hook as PLA or ABS so it can take the weight of heavy shopping bags or full nappy sacks without bending... The 2 parts are very tight and require quite a push to seat together - make sure the screw holes line upwell before joining with M5 16mm machine screws (pan or button head). The screw will form it's own thread though a lot of torque is needed. It doesn't need a nut as the thread is more than tight enough to prevent the screw backing off, and it is only hold the parts together - the flats of the parts are what prevents the hook rotating. My prototype had a nut, but it just added complexity and expense for no clear gain in strength.

The length of the arm was designed around the skoda & vw seats but should fit most modern car seats with removable headrests. The holes are a smidgen under 14mm which is a snug fit, but they can be drilled out quite a lot more if required, if you print with 4+ walls. I added a curved not straight gusset to the hook to avoid leaving a dent in the piping of the seats.

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