Fasteners Chapter 5

Fasteners Objectives Describe USC threaded-fastener measuring system Describe metric threaded measuring system Identify grade markings of threaded fasteners List and describe common thread repair tools

Objectives Identify and explain purpose of common nonthreaded fasteners Explain importance of wire gauge sizes Identify common types of electrical fasteners

Introduction Automotive components are held together with fasteners Much of a technician’s time is spent removing and installing fasteners There are two basic groups Threaded Non-threaded

Threaded Fasteners Most common type of fastener Use spiral threads to wedge parts together Fastener Sizing and Torquing Must be correct strength and size Must be replaced with like size and quality Never install a heavier sheer pin to “fix” a problem

Threaded Fasteners Screws One of the most common threaded fasteners Fits into a threaded hole Different designs to meet attaching needs Some require a wrench to install, others can be installed with screwdrivers Often classed by shape of head

Threaded Fasteners Bolts Use a nut instead of a threaded hole Usually goes through parts that don’t have threads Most have hex-shaped head Two different types Standard Torque-to-yield

Threaded Fasteners Studs Nuts Fastener with no head and threads on both ends Nuts Used with bolts and studs Many different designs Can be specialized to specific applications

Torque-to-Yield Bolt Installation Follow all manufacturer instructions on torquing the bolt Typically first two steps involve an actual ft.lbs reading on a torque meter

Torque-to-Yield Bolt Installation Final step requires tightening the fastener a specified number of degrees Greatly reduces effect of friction on torque readings

Threaded Fasteners Washers Often used to distribute loads Prevent a nut from becoming loose Prevent damage to a machined surface

                                   Washers Flat Spring Lock External tooth lock Internal tooth lock

Nuts

Threaded Fasteners U.S. (English) Thread Sizes Manufactured to Unified System specifications in Fractions of an Inch Threads can be course or fine depending on the number of threads per inch Bolt size is determined by shank diameter, bolt length, and threads per inch

Bolt Identification (Cont’d)

Bolt Identification Diameter Thread pitch (English system) Measured across the threaded area Thread pitch (English system) The number of threads per inch Thread pitch (Metric system) The distance in millimeters between two adjacent threads

Metric Size Bolt Identification Example A metric size bolt that is identified as 6mm x 30mm x 1.25mm: Has a shank diameter of 6 millimeters. Is 30 millimeters long from the bottom of the head to the end of the shank. Has a distance of 1.25 millimeters between its threads.

Imperial Size Bolt Identification Example An Imperial size bolt that is identified as 3/8" x 2" x 24: Has a shank diameter of 3/8 inch. Is 2 inches long from the bottom of the head to the end of the shank. Has 24 threads per inch.

Threaded Fasteners Metric Thread Sizes Same basic measurements as U.S. (English) bolts Pitch number differentiates between fine and coarse as opposed to NC or NF ratings

Measuring Devices (Cont’d) Screw pitch gauge / Thread pitch gauge Is used to determine thread pitch of a bolt or screw. Machinist’s rule Is usually used to measure items that don’t require extremely close tolerances, such as bolt lengths

Bolt Grade Markings Customary (inch) bolts Metric bolts Identification marks correspond to bolt strength. Increasing numbers represent increasing strength. Metric bolts Identification class numbers correspond to bolt strength. Metric and SAE size wrenches are not interchangeable.

Threaded Fasteners Hardness and Strength Strength is identified by grade markings on the bolt head Standards are set by the Society of Automotive Engineers (SAE) Tensile strength is amount of pressure the fastener can take before it breaks

Grade Markings

Threaded Fasteners Fastener Torque Must be tightened to the correct amount Not enough torque causes fastener to loosen Too much leads to breakage

Torque Wrenches

Thread Repair Tools Tap and Die Set Heilicoil Thread Restorer and Chasers Screw Extractor or EZ-Out (Brand Name)

Thread Repair Tools Tap and Die Sets Dies are used to make external threads Taper taps must extend through hole to work properly Bottoming taps thread to bottom of hole

Thread Repair Tools Helicoils Threaded device threads into a hole and provides internal threads for a bolt Must be used in conjunction with a properly sized drill and tap

Heilicoil

Thread Repair Tools Thread Restorers and Chasers Restoring files are used to smooth and shape damaged threads Thread chasers fit over the damaged thread like a fastener Turned back and forth over damaged threads until repaired

Thread Restorer files

TAP

Screw Extractor-EZ Out

Nonthreaded Fasteners Snap Rings Often used to hold parts in place on a shaft Made from high quality steel that retains its shape Snap rings can be internal or external

Electrical Wire Replacement wire must be at least as heavy as the wire being repaired Always try to match wire color Use diagrams to pinpoint wire purpose before repairing

Electrical Wire size

Wire Sizes

Wire Crimpers

Connectors Two types of connectors-Solder and solderless Soldering Best repair method for wires Adds little or no resistance to circuit Use only resin based solder in automotive circuits Acid based solder can add resistance to circuit. Terminal Connectors Device fastened to end of wire, allowing connection to a component Most are covered with an insulator

Connectors Molded and Shell Connectors Many different shapes and sizes Matched in color, shape, purpose to help prevent crossing circuits

Wire Connectors

Connectors Butt Connectors Connects two wires together Quick and easy to install, but may add resistance

Nonthreaded Fasteners Keys Used to retain a part on a shaft Fits into a slot called a keyway Locks the two parts into position

Nonthreaded Fasteners Splines Long teeth are formed onto inside or outside of a part Matching part has splines on opposite side

Nonthreaded Fasteners Rivets Used to hold parts together that are hardly ever disassembled Made from soft materials Rivets are removed by a drill or chisel Then drive shaft out with a punch

Rivets

Summary Threads are measured and classified using U.S. (English) or metric system Fasteners must be used as designed Nonthreaded fasteners are also common Electrical terminals and wiring must be maintained