Chốt Giữ Móc Ikea Hultarp

The black hooks that are available for the Hultarp kitchen rail can easily fall off the rail when jostled. These retaining pins lock into the hole on the hook.  

Print using clone tool to get the number you need. PLA at 100% infill and brim. They are very small and will require some force to push into the hook, try scaling down slightly if you have trouble.