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Available in various finishes for any application
Lag bolts feature a hex head that is designed to be driven with a wrench or hex driver. Lag screws are also commonly called lag bolts because they are significantly larger than most other screws. Essentially, it is just a colossal wood screw with the threads extending to the top. They feature the sharp cutting threads of a wood screw or sheet metal screw and have a shoulder below the head (in longer lengths). However, everything is scaled up in size for use in larger applications. These screws typically need a pre-drilled hole and are not recommended as self-tapping.
Lag bolts are used to lag together lumber framing, to lag machinery feet to wood floors, and other heavy carpentry applications. These fasteners are clearly "screws" when defined by the Machinery's Handbook distinction. The term "lag bolt" has been replaced by "lag screw" in the Machinery's Handbook.  However, in the minds of most tradesmen, they are "bolts" simply because they are large, with external-hex heads. In the United Kingdom, lag screws are known as coach screws.
Lag Bolts vs Lag Screws
Bolts are fasteners with machine thread that can be utilized with a nut. A bolt is appropriately assembled and tightened by spinning the nut. Screws, on the other hand, are fasteners that are correctly installed by spinning the head of the fastener and are typically self-tapping. Despite the different terms, Lag Screws and Lag Bolts are the same fasteners. Technically speaking, Lag Screws is the correct terminology, but you will find many references to them as Lag bolts as well.
Stainless Steel Lag Bolts
Hex lag screws in corrosion resistant 304 stainless steel. Lag screws are basically "large wood screws." A typical lag bolt is a 6 inch long, 3/8 diameter screw with coarse threads of a wood-screw or sheet-metal-screw thread form. Stainless Steel Coach Screws in this selection feature an external hex head. The materials are stainless steel for corrosion resistance. Grade 316 stainless steel lag screws are significantly more corrosion resistant than 304 and are ideal in harsh and saltwater environments.
Hot Dipped Galvanized Lag Screws
Hot dipped galvanized lag screws offer corrosion resistance to steel fasteners due to the molten zinc bath finishing process, creating a bonded alloy coating. The HDG process creates a tightly bonded alloy on the screws for superior corrosion resistance and harsh environment applications. HDG products must be used exclusively when applied, meaning that a plain zinc nut or stainless nut cannot be applied to an HDG bolt. HDG nuts are threaded slightly larger than other nuts to make room for the galvanized coating's thickness.
Silicon Bronze Hex Lag Screws
Hex lag screws in corrosion-resistant Silicon Bronze. A typical screw is 6 inches long with coarse threads of a wood-screw or sheet-metal-screw thread form (but larger). Silicon Bronze Lag Screws in this selection feature an external hex head. The materials are silicon bronze for corrosive, marine, and high heat environments.
Zinc Plated Steel Hex Lag Bolts
Lag screws with a zinc plated finish (CR+3) offer protection to the case-hardened fastener. They are available in standard SAE inch sizes in various lengths. While they have a protected layer of zinc, these screws are not as corrosion resistant as HDG and are not recommended for exterior use.
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What is a lag bolt?
Lag bolts are heavy-duty screws used to connect heavy lumber and other materials that will bear heavier loads. Lag bolts cut their holes and don't require pre-drilling. Functionally, they are larger and stronger wood screws with hex heads.
What is the difference between a lag bolt and a lag screw?
In practice, there is no difference in the terms. They are used interchangeably to refer to the same fastener. Technically speaking, lags should be referred to as screws, not bolts. Traditionally bolts are assembled with a nut and have machine threading while screws are fastened by turning the head and having threads cut into the material. The term bolt also finds use when referring to large screws, and since lag screws are more or less large wood screws, that is the reasoning for the lag bolt terminology.
Where are lag bolts used?
The most frequent application lag bolts find use is in fastening pieces of heavy lumber, or other similar heavy materials, together, typically in heavy carpentry applications. With the smallest size of a lag screw being 1/4" diameter by 1" long, they are well suited to larger applications over most wood screws.
Do lag bolts need washers?
We highly recommend using washers with lag bolts. Washers increase the surface area in contact with the wood or application surface, reducing the chances of the hex head digging into the wood and cracking it while also making the assembly more secure.