Types of Screws, Bolts and Threaded Fasteners

Types of Screws

  • Deck Screws

Deck Screws Our deck screws feature a type 17 point (notched point at the tip) to aid in chip removal during thread cutting which allows for an easy installation in wood and composite deck materials. A bugle head and square drive help to eliminate the stripping effect sometimes experienced with other types of drives.

  • Hex Lag Screws

Hex Lag Screws Lag screws, also called lag bolts, are large wood screws. The head is external hex and are driven with a wrench. Used for lag together lumber for framing, machinery to wood floors, and other heavy duty applications.

  • Self-Drilling Screws Self-drilling screws

Self-Drilling Screws Self-drilling screws have a sheet metal thread with a self-driller cutting (TEK) point to pierce through 20 to 14 gauge metals. The higher the TEK number, the larger the drill point to pierce heavier gauge metals.

  • Sheet Metal Screws

Sheet metal screws (SMS) have sharp cutting threads that cut into sheet metal, plastic or wood. They have a fully threaded shank and sometimes have a notched point at the tip to aid in chip removal during thread cutting.

  • Wood Screws

Wood screws are partially threaded with large cutting threads and a smooth shank. They are designed to slide through the top piece of wood and tightly pull all boards together.

Types of Bolts

  • Hex Head Bolts

Hex Head Bolts: Most common bolt used can be partially or fully threaded. Ideal to drawing two parts tightly together. Example: securing alternator to adjustment bracket.

  • Allen Head Bolts

Allen Head Bolts: Used like the hex head bolt, but is designed to have the head fit into a socket and flush with the surface. Example: through-bolts that secure a windlass to the deck.

  • Carriage Bolts

Carriage Bolts: Clean low profile bolt head designed to “lock” into place using a square counter sunk head. Requires nut to secure. Example: wooden trailer bunk installation.

  • U-Bolts

U-Bolts: “U” shaped bolt with threads on either leg. Ideal for wrapping around one part to secure to another. Example: trailer parts, bow eyes.

  • Eye Bolts

Eye Bolts: Single threaded shank with eye head. Great as a through-bolted pad eye. Example: hold down rings for coolers.

  • Hanger Bolts

Hanger Bolts: Unique fastener that combines the coarse threads of a lag bolt with the fine threads of a machine bolt. These fasteners are typically installed in wood to provide a threaded stud to secure hardware with washers and nuts. Example: motor mounts, steering system brackets.

There is a wide array of threaded fastener types, including:

  • Unified national coarse (UNC)
  • Unified national fine (UNF)
  • Unified national extra fine (UNEF)
  • UNJC and UNJF threads
  • UNR threads
  • UNK threads
  • Constant-pitch threads
Unified National Coarse Threads UNC threads are the most common general fastener thread. Their fit is deeper and more generic than that of a fine thread, allowing for easy removal. Generally, they have a higher tolerance for manufacturing and plating, and do not need cross threading to assemble.
Unified National Fine Threads UNF nuts and bolts have better torque-locking and load-carrying ability than UNC threads because of their larger minor diameter. Because of their more specific fit, they have tighter tolerances, finer tension adjustment, and can carry heavier loads. They are most commonly found in the aerospace industry.
United National Extra Fine Threads A UNEF thread is finer than a UNF thread; they are used in applications with tapped holes in hard material, thin threaded walls, and tapped holes in thin material. As with UNF threads, UNEF threads are common in the aerospace industry.
UNJC and UNJF Threads There are two types of “J” threads: external and internal. External UNJC and UNJF threads have a larger root radius than the corresponding part (either UNC, UNR, UNK, or UNF threads). The larger root radius results in a larger tensile area than the corresponding thread, and smaller stress concentration—bolts that carry heavy loads usually use “J” threads.
UNR and UNK Threads A UNR external thread is the same as a UNC thread, only the root radius is rounded. There is no internal UNR thread. UNK threads resemble UNR threads, but the root radius and minor diameter require inspection.
Constant-Pitch Threads These threads come in a variety of diameters to fit a given application—bolts with diameters of 1 in. and above commonly use pitches of 8, 12, or 16 threads per inch.
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