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 assortment range from M3-0.50 to M6-1.00 in coarse thread size and range from 6mm to 30mm in length. Full assortments of #3606 contain sixteen (16) refills comprised of Hillman item numbers #3607 - #3622.