Masses with hooks on both sides allow you to hang the weights to each other as well as to other instruments. Made of brass and some of them may be plated with nickel as shown in the image. The bottom hook in larger masses are recessed and will not be visible while seated on a flat surface.
If you need Masses with hooks on one side please use the product code 3406B.
You may also buy a complete set of masses with hooks. This is listed as Masses with hooks, set of 9 with product code MASSET9H. This set also includes a holder.