The BiMetal caps are made of both tin and aluminum and are easier to crimp than tin 20mm seals. The sealing surface is aluminum and the inner diameter is made of tin to add the magnetic surface. These caps are available in a variety of colors.
Other Notes: We recommend using the plier-type decapper (part number 33283) to remove the bi-metal crimp seal. Due to the mechanics of the decapper, the plier-type decapper is less expensive and works better that the Hand Decapper (p/n 33283) for this application.