Concertina Razor Coils Crossed Concertina Razor Coils Concertina coils are the most popular high security fencing for military and high grade residences safety. Two main types available for concertina coils: one is the single coil and the other is crossed concertina coils. Crossed concertina offers the highest security grade among all the razor wire fencings. Concertina type razor coil wire is installed without clips and it runs in natural loops on walls. It costs less with easy installation. Materials: Galvanized steel sheet, stainless steel sheet.