Hook for Artiteq Click Rail picture hanging system (schilderij ophangsysteem)

NOTE: The design which can currently be downloaded proved not to be strong enough. Don't build this. Wait a few days and I'll upload an improved design after I've tested it for a while with weights.

This hook allows pictures to be hung from the Artiteq picture Clickrail system. While the official hooks are rated for 4 kg and higher I wouldn't expect this hook to take a huge weight, but it does seem to be strong enough for small pictures and it fits into the rail just like the official items.