Lockbolts Information

Lockbolts are two-piece fasteners that consist of a headed, parallel-shank pin with a serrated end and collar. An assembly tool is used to swage the collar onto the serrated grooves in the pin and break the stem flush to the top of the collar. Shear strength, tensile strength, collar style, grip range, and diameter are important specifications to consider when selecting lockbolts. Shear strength, the resistance to transverse loading, is expressed as force in Newtons (N) or pounds (lbs). Tensile strength is the amount of longitudinal load a lockbolt can withstand before failure. There are three collar styles for lockbolts: standard, low profile, and flanged. Most suppliers specify shear strength and tensile strength with a standard or full collar. The use of a low profile collar (half collar) increases the pin’s grip range, the minimum and maximum thickness of the materials or parts that a lockbolt is designed to secure. Typically, a half collar reduces the tensile strength by about 45%. Flanged-head collars can be used when the hole on the collar side is oversized or slotted.

Lockbolts differ in terms of head diameter, body diameter, and head style. Dimensions are measured in English units such as inches (in) or metric units such as millimeters (mm). There are many different head styles. Brazier heads are oval-shaped. Cone or pan heads have a high profile. Countersunk heads or flush heads are used with flush surfaces. Dome heads or button heads have a low profile and are the most commonly-specified head style. Flat head lockbolts have a conical bearing surface and can be countersunk or flush. Large flange-heads have twice the underhead bearing surface of dome heads. They are designed to join soft or brittle materials to rigid backings. Lockbolts with a mushroom-shaped head have a large, underhead footprint to distribute the load on softer materials. Truss heads are used in applications which require a low- profile head. Universal heads are usually oval-shaped. Some manufactures refer to universal heads as mushroom, brazier, oval or truss heads. Round-head lockbolts are also available.   

Lockbolts are made of a variety of metallic and non-metallic materials. Metal lockbolts are usually made of aluminum, brass, bronze, copper, steel, hardened steel, stainless steel, or titanium. Lockbolts that are made of proprietary alloys such as Monel®, Inconel® and Incoloy® (Special Metals Corporation) are also available. In some cases, manufacturers apply protective coatings or finishes to improve corrosion resistance or surface adhesion. Some metal lockbolts are anodized or galvanized. Others are plated with brass, chrome, gold, nickel, silver, or tin. Fasteners with black oxide, phosphate, and zinc chromate coatings are also available. Non-metallic lockbolts are usually made of plastic, thermoplastic or rubber materials. Materials of construction include fiber-reinforced plastic or fiber-reinforced polyurethane (FRP), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

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