Hillman Round Head Machine Screw, 6-32 x 3/8 In. Machine screws are designed to fasten metal parts together securely, either by using nuts or by screwing directly into a threaded receptacle. The length of the fastener is measured from the underside of the head to the tip of the screw, ensuring precise fit for your project. For optimal performance, it is to use nuts that match the screw’s finish and threading. Model Number: