 Antimony forms a highly useful alloy with lead , increasing its hardness and mechanical strength . For most applications involving lead , varying amounts of antimony are used as <unk> metal . In lead – acid batteries , this addition improves the charging characteristics and reduces generation of <unk> hydrogen during charging . It is used in <unk> alloys ( such as <unk> metal ) , in bullets and lead shot , cable <unk> , type metal ( for example , for <unk> printing machines ) , <unk> ( some " lead @-@ free " solders contain 5 % Sb ) , in <unk> , and in <unk> alloys with low tin content in the manufacturing of organ pipes . 
