Studs

Studs are metal rods that are threaded at both ends (refer to figure below). In general, they are used where it is not possible or desirable for a bolt to be used. Like many screw types of fastener, most studs are produced in a standard form with variants used for special purposes. For example, where a standard type is unsuitable, such as when being used in a soft metal, then a stepped stud (which has a greater holding power) would be used. A stepped stud would also be used where a damaged thread had been removed, the hole drilled out and re-tapped.

It will be appreciated that the security of a stud depends upon the friction between its thread and that of the tapped hole (the ‘metal’ thread) into which it is inserted. If this friction fails to hold the stud, it will work loose and all precautions to prevent the nut from slackening will be negated.

FIGURE

Standard Studs

By far the most widely used stud is the standard (plain or parallel) type, in which the diameter of the whole stud along its length is constant. Standard studs are classified by the thread type, diameter and overall length. Usually, the ‘metal’ thread is finished very slightly oversize to give a tight fit into the tapped hole. Other variants of the standard stud are available for use in circumstances that require special consideration.

To meet special requirements, the various types of standard studs may also be supplied with non-standard lengths of plain portion and ‘metal’ end. A simple method of fitting and removing a stud is by running two plain nuts down the ‘nut’ end of the stud and cinching (locking) them together using two spanners. The stud can then be screwed into or removed from the material. Breaking the cinch, then separating and removing the nuts completes the operation.

Waisted Studs

Waisted studs are used where reduction of weight without the loss of strength is of paramount importance. The diameter of the plain portion of the stud is reduced to the minor diameter of the end threads, thus lightening the stud without impairing its effective strength.

Stepped Studs

This type affords a stronger anchorage than the standard type, if the ‘metal’ end of the stud has to be housed in soft metal. The thread of the ‘metal’ end is one size larger than that of the ‘nut’ end. For example, a ¼ inch BSF stepped stud has a plain portion of ¼ inch thread on the ‘nut’ end and a 3/16 inch thread on the ‘metal’ end.

Stepped studs are also used as replacements for standard studs when the tapped stud-hole has to be re-drilled and tapped with a larger thread due to damage.

Shouldered Studs

This type is used where maximum rigidity of assembly is of prime importance. The stud is machined from oversize bar and a projecting shoulder is left between the ‘metal’ end of the thread and the normal diameter plain portion. This shoulder seats firmly on the surface of the ‘metal’ and gives additional resistance to sideways stresses. The clearance hole in the second component through which the ‘nut’ end and plain portion of the stud passes, must be machined at the inner end to give clearance to the stud shoulder.