4 Pc Red Spark Plug Wire Protector/Insulator Shield Sleeve/Boot 1" Inch for Ford Mustang This is a set of 4 sleeves Sleeves are 175mm (6.8") long. Diameter of opening on ring side is 18mm (.7"). Open side is 25.4mm(1") without stretching the product. Made from glass fibers, heat rated up to 593 degrees Celsius (1100 degrees Fahrenheit).