Disclosed are immobilized dimercapto succinate compounds, a method to synthesize these immobilized dithiol compounds, and a method of using the immobilized dithiol compounds to remove metals, such as lead, cadmium and mercury from an aqueous solution. In some embodiments, positive stopping apparatus on the crimp ring are used to assure appropriate closure of a crimp ring assembly. The spacer has a joint face engaging with the lower face and a mounting face opposite to the joint face.