Machine screws are used in conjunction with washers and hex nuts in order to fasten metal parts together securely. To ensure proper fit and quality of life, make sure to use machine screws with nuts of similar thread size and finish. Variants included in this Knurled-Head Machine Screws Assortment feature a coarse #8-32 thread size and range from 1/2" to 3/4" in length. Full assortments of #54066 contain eight (8) refills comprised of Hillman item numbers #54067 - #54074.