ROCKBROS roof rack inserts for 91mm hub kids bike

These inserts/adapters allow the roof rack to carry childrens bicycles with 91mm wide front axle hubs. Made to fit a 16" PUKY kids bike, but it should fit universally for kids bikes or vintage/entry level bikes with 91mm fork/hub spacing (the ones with solid axle front hubs with cap nuts).

These inserts need to be much narrower than the original ones (4.5mm each to be exact, since the fork is made for 91mm wide axles instead of 100mm). Because of that the outer lip is less than 2mm thick. With the original inserts, the entire clamping force of the quick release axle is supported on this lip, which in this narrower version is now less than half the thickness. 

To prevent this lip from colapsing under pressure (resultung in loss of clamp force and the bike no longer being properly secured) I extended one insert, so that both inserts butt together inside of the tube. This way, the axle tension load is being transfered through this cylinder piece rather than over the lips. The lips are only there to center the bike in the rack while driving through curves but are no longer stressed by the axle tension. I've been using this for more than 200km with no issues now - still, use at your own risk!

Printed mine with PETG and works fine. ASA/ABS would propably be even better. 
I do not recommend using PLA.

No additional parts needed. Use the O-Rings and quick-release skewers from the original inserts.