Made of 304 stainless steel, durable, corrosion resistant, high hardness 7 Common Sizes for general use, including: M3, M4, M5, M6, M8, M10, M12 ;Versatile use, ideal for professionals and amateurs alike Nylon insert lock nut features an integrated system of nylon that grips bolts to prevent loosening Collar nylon can prevent the bolts from coming out for a more secure and durable hold Package quantity is 165pcs, in a clear plastic box for storage