MECHANICAL FASTENERSTYPES AND APPLICATIONS

INTRODUCTIONMechanical fasteners include nuts and bolts, screws, solid rivets, pop-rivets and a wide variety of devices for securing components together.

They are most often used for securing parts that may have to be adjusted or removed in order to repair or replace them.

TYPES OF FASTENERSThey can be divided into two groups:

Those that require access to both sides, like a nut and bolt where a spanner is needed on both the nut and the bolt.

Those can be secured from one side as with a pop-rivet, self-tapping screw or a setscrew screwed into a captive nut.

BOLTSBolts have a plain shank to pass though the components and a short threaded portion for the nut that goes on the end.The size shown on a metric spanner indicates the width across the flats of the nut or bolt head.

SETSCREWSAre threaded along the whole of their length which reduces the need to have bolts of different lengths.

They can be screwed into a captive nut until the parts are pulled together.

NUTSThere are several types including castellated nuts that use a split pin or wire to secure them in place.

NYLOC NUTSThe nyloc nut has a nylon insert that grips the thread

FLAT WASHERSFlat washers spread the load and prevent the nut or bolt marking the component.

SPRING WASHERSSpring washers are made of hardened steel, they have sharp edges that cut into the surface and prevent nuts from working loose.

SHAKEPROOF WASHERSThese are designed to grip the surface of the component and the underside of the nut to prevent them from coming loose.

SELF TAPPING SCREWSThese are used to fasten removable vehicle body components in place, they can be screwed directly into the material that they are securing together because they cut their own thread.

SLOTTED SCREWSThe correct screwdriver must be used to avoid slipping and damaging the slot

PHILLIPS SCREWSThese have slightly rounded corners in the tool recess, and are designed so the driver will slip out, or cam out, under high torque to prevent over-tightening.

POZIDRIVE SCREWSAre similar to Phillips, the advantage it offers is that, it does not cam out, allowing great torque to be applied.

ALLEN SCREWSAllen Screws use an hexagonal key, they are often used for countersunk or recessed fasteners.

TORX SCREWSTorx fasteners use a splined tool, there are internal and external types.

CAPTIVE NUTSAre used to speed up assembly times and where access is difficult or impossible on the other side of the component.

They come in several types, nuts that are welded or riveted in place, nuts that are secured in a metal bracket or clip.

Plastic blocks, spring steel clips, often referred to as spire speed nuts and threaded metal plates secured within car doors and hinge pillars etc.

CAPTIVE NUTSA wide range of captive nuts include those that secured by metal cages, welded, crimped and plastic blocks.

BODY PANEL BOLTS

SPIRE SPEED NUTSThese are often used in conjunction when self-tapping screws are used to secure plastic or sheetmetal components, making them more secure and less likely to work loose or pull through.

SPIRE SPEED NUTS

POP RIVETSAre often used to secure body panels and trim, but are not suitable for securing heavy components.

PLASTIC TRIM CLIPS

These come in a wide range of types some can be reused but many of these need to be renewed as they are often damaged if they have to be removed.

INTERIOR TRIM CLIPS

WING LINER FASTENER