Threaded fasteners are used for many applications so although their function is simple – to hold components together – there is a wide variety of designs and sizes. There are specific designs for applications where the fastener needs to be very strong, such as for machine applications.

Mechanical Bolt Forces Clamping Force: This is a type of compression that the bolt applies to the joint, holding the two components together. Preloading Force: Turning the bolt causes the threads to engage and stretch, which produces the preload force that keeps the threads in place.

“Heading 7318 of the Harmonized Tariff Schedule of the United States (HTSUS) provides for ‘screws, bolts, nuts, coach screws, screw hooks, rivets, cotters, cotter pins, washers (including spring washers) and similar articles, of iron or steel.

A threaded fastener has internal or external screw threads. The most common types are the screw, nut and bolt, possibly involving washers. Other more specialized types of threaded fasteners include captive threaded fasteners, stud, threaded inserts, and threaded rods.

There are three main types of threaded fastener; Bolts, Screws and Studs. Bolts have a head on one end (this is usually a hex head) and are threaded on the other. They are generally used in conjunction with a nut (and sometimes a washer) to hold them in place.

The 3 Primary Types of Threaded Fasteners

• #1) Screws. The most common type of threaded fastener is a screw.
• #2) Nuts. Another common type of threaded fastener is a nut.
• #3) Bolts. The third primary type of threaded fastener is a bolt.

There are two types of threads to be managed in a modern system: User threads and kernel threads.

The most common thread types are the inch-based Unified coarse / fine (UNC/UNF) and metric coarse / fine. Other types and their purposes are described at the end of this section.

ACME threads are commonly used in clamps, vises, and linear actuators. The main advantage to an ACME thread is a low number of threads per inch. This allows ACME threads to allow for increased linear actuation per turn of screw which is similar to a square thread.

Two types of buttress thread profiles used in machinery.

A way to distinguish between NPT and Buttress is by their appearance. Buttress threads have a thread where there the lines are spaced further apart making them look more coarse. So they are sometimes called “coarse threads”.

The buttress thread form is designed to handle extreme high axial thrust in one direction. This is typically a 7° angle on the weight bearing surface and a 45°angle on the trailing flank, which provides a form with good shear strength.

The acme thread form is most often associated with lead screws or CNC drive systems , and for good reason. These threads are broader, stronger, and squarer than standard V-shaped threads. This makes them ideal for power transmission and carrying loads.

Which of the following is true for the multiple start screw threads? Explanation: Multiple start screw threads is produced by forming two or more than two helical grooves, equally spaced and similarly formed in an axial section on a cylinder. This gives a ‘quick traverse’ without sacrificing core strength.

The standard international metric thread eventually evolved from German and French metric standards based upon a 60 degree V thread with flat crests and rounded roots. The most common screw thread form is a symmetrical V-Profile.

What is the relation between rate of wear and contact surface area? Explanation: If any surface has large number of irregularities i.e. hills and valley then the surface will obtain good bearing properties. Rate of wear is proportional to the load per unit area and surface area in contact.