The screws in the picture are for furnitures and have absolutely no place in a bike =)
 

Sure. The original one on the right was shipped with the trailer so I would have assumed it to be durable enough. I may have broken the weight limit of 70kg though, which might explain why they broke in the first place. Now I'm going with slightly thicker steel screws which seem to be holding up okay, especially since I have no need to overload.