Chapter 3 Fasteners Objectives Identify types of threaded

Chapter 3 Fasteners

Objectives • Identify types of threaded fasteners. • Identify the parts of a bolt. • Identify a bolt by diameter, threads per inch, length. • Identify types of bolts. • Identify nuts. Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Objectives (Cont. ) • • Identify locking nuts. types of screws. types of washers. various nonthreaded fasteners. Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Fasteners • Simple devices that hold parts together or in place • Fasteners connect – Metal to metal – Plastic to plastic Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Types of Fasteners • Threaded fasteners – Use screw threads to tighten two components together • Mechanical fasteners – Use mechanical force or process to hold parts together or make connection with component – Retainers limit component’s movement while allowing it to slide, pivot, or rotate Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Threaded Fasteners • Thread – Inclined plane wrapped in helix around central axis – Converts rotational movement to linear • Typical rotation – Clockwise rotation tightens fastener – Counterclockwise rotation loosens fastener Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Linear Movement and Rotation Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Special Applications • Some applications require reverse threads – Left-hand threads – Slope downhill left to right – Opposite incline to right-hand threads – Tighten by counterclockwise rotation – Loosen by clockwise rotation Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

External Threads • Formed on outside of fastener • Allow fastener to be screwed into threaded hole or nut Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Internal Threads • Formed inside of hole • All nuts have internal threads Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Bolts • Externally threaded fasteners – Pass through holes in two or more parts – Parts are joined when nut is tightened onto bolt – Most bolts must be held to tighten nut – Consist of threads and shank Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Screws • Externally threaded fasteners – Pass through hole in one part – Thread into internally threaded hole (or form their own threads) in second part • Tightened or released by rotating head Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Bolts vs. Screws • Screws – Fasteners with thread diameters of less than 1/8″ • Bolts – Fasteners with thread diameters larger than 1/8″ Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Machine Screws • Thread into another component • Standard coarse and fine thread • Can be used with nuts – Both made in standard sizes – Conform to each other Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Non-Machine Screws • Threads on screw cut matching threads in material into which it is tightened • Used on plastic or soft metal • Coarse threads on fasteners provide holding power Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Tapping (Cutting Threads) • Process of cutting threads in hole • Tap tool (tap) is used to cut internal threads Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Bolts and Machine Screws • Head and body – Body is divided into threaded portion and shank – No shank if threads go completely to head Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Bearing Surface • Area underneath head – Usually flat and smooth to reduce friction – Applies clamping force to components being tightened • Cap screw (round bearing surface) • Flat head fastener (tapered bearing surface) Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Bolt and Screw Designations • Designated by one or more – Thread form nomenclature – Type of head drive system – Special features Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Thread Form Nomenclature • Identifies fasteners by – Diameter – Threads per inch – Length • Conforms to either – US customary thread form system – Metric thread form system Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Thread Standards • Terms to identify conforming threads—Unified National threads, inch threads, English threads • Conforming thread standards are set by – ASME – ANSI – IOS • Standards set for fastener diameter and threads per inch Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Bolt and Machine Screw Identification • US customary bolts and machine screws are identified by – Diameter – Threads per inch (tpi) – Length • Format – Diameter threads per inch × length Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Metric Bolts • Identified by – Diameter (in millimeters) – Pitch • Pitch – Distance from tip of one thread to tip of next – Amount of linear distance that fastener moves in one revolution Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Metric Bolt Identification Format • Format (in this order on head) – Capital M – Bolt body diameter in millimeters – Dash (spoken as “by”) – Thread pitch • Example: M 8– 1. 25 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Metric Bolt Identification • Standardized diameters and thread pitches • Identified by pitch – Smaller number after dash means more threads per bolt – If no pitch, default is coarse thread pitch • Multiplication symbol and following number indicates bolt length Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Bolt and Screw Identification • Type of head, drive system, or combination • Head shape determines type of head – Hexagonal (hex)-shaped – Square – Pan-shaped – Flat Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Hexagonal Head Fasteners (Flats) • Can be held or rotated using standard wrenches because of standardized head dimensions • Distance across two opposite sides of head conforms to standard size established for bolt thread diameters Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Hex Flange (Washer) Head Fasteners • Washer integrated with head – Increases bearing surface – Distributes torque load over larger surface area than standard hex head Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Serrated (Binding) Head Bolts • Raised serrations on bearing surface lock into surface of component – Prevents bolt from loosening or backing out • Angled serrations keep vibrations from loosening bolt Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Square Head Fasteners • Four-sided head fits into square opening • Not necessary to hold head with wrench while tightening nut • Exposed threaded end used as stud Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Types of Screw Heads Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Drive Systems • Hexagon socket head – Hex head, socket head Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Drive Systems (Cont. ) • Torx-type (hexalobular) – Size designated by “T” followed by number • External (reverse) Torx fastener – Size designated by “E” Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Drive Systems (Cont. ) • Cross-recessed drive – Phillips-type – JIS Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Drive Systems (Cont. ) • Combination drive systems Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Special Feature Fasteners • Threaded fastener with unique design • Intended to be used for specific applications Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Stud • Usually threaded at both ends – One end installed in part – Other end accepts nut • Different thread type on each end Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Stud Bolt • Head is anchored in part • Threaded end protrudes to act as stud Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Square Shoulder (Carriage) Bolt • Shoulder located directly under head • Inserted into preformed hole in one component so nut can be applied to threaded end to attach second component Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Hex Socket Head Shoulder Screw • Hex socket recess in head • Round shoulder shank diameter is larger than fastener thread diameter Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

SEMS Fastener • Washer is permanently attached to screw, bolt, or nut • Fastener and washer are installed in one step Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Set Screw • Threaded fastener used to mechanically hold two components in position with each other • Usually does not have head • Intended to be installed flush with or below surface Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Self-Threading (Thread Forming) Screw • Special threads and ends displace and reshape material, forming internal threads • Normally used in soft metals and plastics • Can be used to produce machine threads or screw threads • Internal threads formed during installation are permanent Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Self-Threading (Thread Forming) Screw (Cont. ) • When screw is reinstalled, threads must screw into original internal threads • To align screw with original threads – Rotate screw backward by hand until it clicks – Rotate screw clockwise to tighten Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Sheet Metal Screw • Fastens thin metal sheets or light-duty plastics • Self-threading • Internal threads remain after screw installed Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Thumb Screw • Screw with special designed heads • Tightened and loosened by hand Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Nut • Internally threaded fastener that screws onto externally threaded fasteners – Applies holding torque to keep components together under normal vibration – Bolts pass through two components and use a nut to keep parts together Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Typical Nuts • • Hex nuts Square nuts Locknuts Finger-tightened nuts Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Hex Nut • Six-sided nut that screws onto bolts • Identified by thread form Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Flange Hex (Hex Washer Head) Nut • Washer bearing surface on one side of nut – Distributes tightening force over larger surface area – Nut can be torqued to higher value Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Locknut • Nut deformation or insert keeps nut from spinning freely and backing off Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Wingnut • Designed to be installed and tightened by hand Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Washers • Flat washer – Thin disc with hole in middle – Used between • Surface of components and nut • Surface of components and fastener head – Allows large clamping force without damage Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Washers (Cont. ) • Lock washer – Keeps fasteners from loosening – Can be used to improve electrical connections Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Thread Adhesive • Applied to fastener threads to prevent loosening due to vibration • When fastener is reinstalled – Remove old adhesive – Reapply fresh adhesive with same holding power • Color indicates qualities (strength, heat resistance, penetrating ability) Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Adhesive Fasteners • Threaded fastener with correct amount of adhesive preapplied • When fastener is installed, friction from tightening releases adhesive • Also called microencapsulated fasteners Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Removing Cured Adhesive • Dried adhesive must be removed from threaded hole • Determine – Fastener thread form and diameter – Thread pitch • Select tap with same thread type • Thread tap into hole to remove old adhesive Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Thread Repair • Restoring threaded hole to its original thread form • Metal threaded insert may sometimes be installed • To repair threaded holes, follow manufacturer’s repair procedure Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Torque System • Torque – Twisting force that tries to rotate fastener – Stress keeps fastener tight (torqued) • If torqued too much, fastener could break or components could be damaged • If torqued too little, fastener could loosen during operation Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Correct Torque • Torque must be enough to – Stretch fastener without breaking it – Hold components together without damage • Torque must not exceed strength of fastener • Correct process must be used Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Need for Torque • Vibrations from engine add stress parallel to center of fastener • Screw tends to back out of threads • Nut tends to unscrew from bolt Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Thermal Expansion • Components expand when engine heats up and contract when engine cools off, causing fasteners to loosen • Thermal expansion and contraction varies in different parts of engine • Same fastener used in two locations may require two different torque values • Follow manufacturer’s torque requirements Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Engineered Stretch • Fasteners are able to stretch and remain under tension • Fasteners return to original shape when loosened • Amount of stretch is engineered to adequately hold each piece of equipment in place • Strength of fastener affects amount of torque applied Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Torque Specification • Torque specification must account for – Elastic limit – Tensile strength • Torque value cannot be greater than elastic limit Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Sustaining Torque • Ability of threaded fastener to sustain torque through threads depends on – Diameter of fastener – Number and type of threads – Grade of material • Tensile strength is determined by – Minor diameter of fastener – Fastener material Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Fastener Grade • Indicates metal alloy composition of fastener • Composition contributes to elastic limit and tensile strength • Higher grade bolt has greater strength but lower elasticity than lower grade bolt Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Torque Wrench • Torque applied to fastener—a force acting at a distance from the center of the fastener • Torque is applied and measured with torque wrench • It is important to read and understand torque wrench instructions Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Selecting Torque Wrench • Identify torque specification units for fastener – In-lb (inch-pounds) – Ft-lb (foot-pounds) – N·m (newton-meters) • Select wrench that – Can measure needed units – Includes torque range to be measured Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Tightening in Proper Sequence • Follow equipment manufacturer’s torque sequence – Some fasteners can be torqued in one step – Others must be torqued in stages (especially for high torque values) • Install fasteners before tightening any of them Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Nonthreaded Fasteners • Connect two parts together to make one assembly – Use mechanical holding process other than threads – May have threads, but threading is not primary means of connection Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Clamps • Circular flat metal or wire bands • Apply pressure to one component to keep it fastened to another component • Types of clamps – Wire clamp – Spring clamp – Rigid clamp – Flexible hose clamp Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Wire Clamp and Spring Clamp Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Rigid Clamp and Flexible Hose Clamp Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Spring Safety Hooks (Clasp) • Connect parts together loosely • Spring keeps it closed when attached • Can be quickly taken on and off by – Depressing spring – Hooking or unhooking clasp Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Dowels and Sleeves • Dowels (or dowel pins) – Solid metal fasteners used to perfectly align two parts – Usually slip into mating hole with just enough clearance to enter without friction or looseness • Dowel sleeves are similar to dowels, but hollow Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Retainers • Keep a component in place • Either lock onto something or lock in place inside something Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Types of Retainers • Push-on retainer – Round press-on clip that holds two parts in place – When pushed onto shaft, spring-loaded tabs press into surface, locking retainer in place • E-clip retainer – Slides into grooves on outside of shaft and locks in place Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Clips • Hairpin clip • R-clip Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Snap Rings • External – Fit into grooves to retain parts on shaft • Internal – Installed into grooves inside a bore Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Circlips • Circlips (hookless snap rings) – Assembled into an internal groove in a bore – Keep wrist pins in place Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Roll Pins • Spring steel rectangles rolled into cylinders • Driven in place; held in place by spring pressure • Used to lock parts in place Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Cotter Pins • • Used to retain components on a shaft Split pin retainers Inserted through hole in shaft Ends are spread to keep pin from backing out Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.