Fastener BasicsCommon Fastener TypesFastener MaterialsHex bolts, or hex cap screws, are used in machinery and construction. Can be used with a nut, or in a tapped hole. Fully threaded hex bolts are also known as tap bolts.Wood screws have large threads and a smooth shank f or pulling two pieces of material together. They can be used in wood and other soft materi-als.Sheet metal screws have sharp points and threads, and are designed to be driven directly into sheet metal. They can also be used in softer materials like plastic, fiberglass, or wood.Machine screws are fully threaded for use with a nut or in a tapped hole. Certain types are some-times referred to as stove bolts.Socket screws are machine screws with an internal hex socket (Allen) drive. Longer lengths may have a smooth shank.Lag bolts, or lag screws, are large wood screws with hex heads. Typically used for wood construction and landscaping.Carriage bolts have smooth, domed heads with a square section underneath that pulls into the material to prevent spinning during installation.Nuts are used to fasten machine threaded fasteners in through-hole applications. Lock nuts help prevent loosening.Washers spread the load over a greater surface area when tightening a bolt, screw or nut. Lock washers help preventing loosening.Tip: Find a more comprehensive fastener type chartGrade/Class & Fastener StrengthFastener Grade (US) or Class (metric) refers to the mechanical proper-ties of the fastener material. Generally, a higher number indicates a stronger, more hardened (but also more brittle) fastener.For a chart of fastener grades, head markings and mechanical properties, see Bolt Depots Grade markings and Strength ChartUS bolt head markingsMetric bolt head markings8.810.912.9Low CarbonGrade 5Grade 8Class 8.8Class 10.9Class 12.9Note: In addition to these markings, the head will often have a manufacturer stamp.Note: Do not rely on this guide for color-matching. The appearance of these materials sometimes di ers signifi-cantly from the photos below.Zinc-plated steel is a low carbon steel for general use. Relatively inexpensive, with the zinc plating providing moderate corrosion resistance suitable for indoors or otherwise dry conditions. Color is either a blue-ish tint oryellow depending on the exact process.Hot-dipped galvanized steel has a thicker zinc coating for better corrosion resistance, making it suitable for outdoor use. Because of the thick plating,only galvanized nuts and washers will fit galvanized bolts. The coating typically has a rough, dull grey finish.Stainless steel o ers good corrosion resistance, making it suitable for outdoor use and marine applications, but ismore expensive than zinc plated.Chrome and nickel plated steel are smooth and polished for appearance. Theplating o ers moderate corrosion resistance.Brass and bronze are copper alloys with good corrosion resistance. More expensive than steel, these materials are typically used for decorative applications. Colors can vary significantly.Alloy steel is highly hardened and usually black oxide and/or oil coated, o ering little corrosion resistance.Page 1How Fasteners are Notated: An ExampleMachine screws, Phillips pan head, Stainless steel 18-8, #12-24 x 1FastenertypeMaterialDiameterLengthThread Count (TPI)Drive TypesHead StylesMeasuring DiameterPhillips SlottedComboFrearson PozidrivHex socket(Allen)StarSquare(Robertson)Phillips and Slotted drives are common in screws, but prone to cam-out (stripping).Combo drives, that can be used with either driver, areavailable for many fastener types.Frearson and Pozidriv are similar to Phillips, but less prone to cam-out.Hex socket (Allen) drives are compact and easy to drive, but prone to cam-out.Star and Square drive are resistant to cam-out and can be installed single-handed.Hex heads are typically used with larger bolts and screws, and tightened with a wrench.Pan heads have a slightly domed head that sits above the surface.Flat heads are installed in a countersunk hole for a flat surface.Round heads are tall domed heads, used primarily for decorative purposes.Oval heads are a low domed and countersunk heads, used primarily for decorative purposes.Truss heads are slightly domed, with a wide head for an extra large surface area.Socket heads are narrow with a socket drive, and knurled or smooth sides.For most types of fasteners, the diameteris measured on the outside of the threads.Note: US diameters under 1/4” are given as numbe