Black ABS plastic cap. 300 series stainless steel backplate (0.015 Inch T). Manufacturing date code is stamped into stainless steel back plate. 4 mm snap stud machined from 300 series stainless steel. Fits to 4 mm spring loaded medical type socket. Coil cord disengages from snap with 1 - 5 lb. of perpendicular force. Durable, providing long life well beyond that of sheet metal snaps. - Premium metal expansion wrist strap. Inside links are constructed of 300 series stainless steel. Width of links is 0.63 Inch, 0.002 Inch polyphenylsulfone sheet is laminated to each link before assembly. Provides >5000V rms insulation per ASTM D149. Will not flake or peel.