Machine screws 101

A machine screw is ¼" nominal diameter or less, threaded uniformly, and designed to be threaded into uniformly threaded holes or threaded nuts in the parts they are fastening. 

Machine screws are essential fasteners used in many industries including marine, automotive, and aerospace. Also known as metric screws, they're used to attach many important pieces of engines, foils, extremities, etc. So making sure you order the right fastener is important! Simply follow this step-by-step guide to make sure you're getting what you need.

Machine Screw Diameters

Sizing - Sizing machine screws correctly is a difficult procedure that needs to be done with some accuracy. To get the diameter, use calipers or a fastener guide. Measure from the outside of the thread and use the chart above (for standard sizes). Metric fasteners correspond with the appropriate millimeter measurement.

Along with screw length, you'll need to determine thread count and length. Thread count is determined by the number of threads per inch (or # of threads / 1/4 inch * 4). Length is measured depending on the head style. Flat head and oval heads (and anything else countersunk) is measured from the top of the machine screw. All other styles are measured from beneath the head.

Drive Head Types - Machine screws are available with different types of heads. The most common ones are flat head, pan head, oval head, round head, hex head, and truss head. Please refer to Choosing the right driver/fastener head, a simple guide with pictorial references and descriptions of the head styles.

Metal - We specialize in four types of metal finishes in our fasteners: Stainless Steel, Silicon Bronze, Brass, and Galvanized. To determine the appropriate metal for your machine screws, please refer to Fastener metals explained and Compatible metals finder.