Kahtoola MICROspikes Traction System Spike Material: heat-treated 400 series stainless steel Sizing for running shoes/hiking boots: [X-Small-Youth 1-4] [Small-Youth 4.5-7, Women 5.5-8.5] [Medium-Women 8.5+,Men 7-10.5] [Large-Men 10.5-14] [X-Large-Men 14-16] Sizing for insulated boots: [Medium-Women 7.5-10, Men 6-8.5] [Large - Women 10-12.5,Men 8.5-11] [X-Large-Men 11-13.5] 3/8" spikes are constructed of hardened stainless steel for maximum durability Tough elastomer shoe harness secures easily without straps and provides a snug and secure fit