10-3 Common Threaded
Fasteners
•Machine screws have either fine or course threads and are available in a
variety of heads. They may be used in tapped holes or with nuts
•Cap screws are threaded fasteners that join two or more parts by passing
through a clearance hole in one part and screwing into a tapped hole in the
other.
•Captive screws remain attached to the panel or parent material even when
the mating part is disengaged. They are used to meet military requirements,
prevent screws from being lost, or speed assembly & dis-assembly or prevent
damage from loose screws falling into moving parts or electrical circuits.
• Tapping screws cut or form a mating thread when driven into preformed
holes
• A bolt is a threaded fastener that passes through a clearance hole into a
nut
• Studs are shafts threaded at both ends
THREADED FASTENERS
SCREWS
Head styles
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Hex and square
Pan
Binding
Washer
Oval
Flat
Fillister
Truss
12 point
THREADED FASTENERS
BOLTS
THREADED FASTENERS
STUDS
Drawing a nut and bolt
• Nuts and bolts may be drawn on some
assembly drawings
• Conventional drawing practice is to show the
nuts and bolt heads in the across-corners
position in all views
• Approximate head proportions are shown on
the next two slides
THREADED FASTENERS
HEAD PROPORTIONS
THREADED FASTENERS
HEAD PROPORTIONS
Point styles
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The point of a fastener is the configuration of the end of the shank
Cup
Flat
Cone
Oval
Half-dog
Property classes of fasteners
Inch and metric
• Inch fasteners: the strength is determined by
the size of the fastener and the material from
which it is made. Property classes are defined
by SAE or ASTM. Table 10-1 lists properties
• Metric fasteners: the property classes are
designated with numbers with increasing
numbers generally representing increasing
tensile strength.
Nuts
• Style 1 and Style 2 for metric nuts have
replaced the terms regular and thick
• A locknut is a nut with special internal means
for gripping a threaded fastener to prevent
rotation
• Captive or self-retaining nuts provide a
permanent, strong, multiple-thread fastener
for use on this materials
Washers
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Flat
Conical
Helical spring
Tooth lock
Spring
Terminology
• Tap drill size for a threaded (tapped)hole is a
diameter equal to the minor diameter of the
thread
• Clearance drill size permits the free passage of
a bolt is a diameter slightly greater than the
major diameter of the bolt
10-4 Keeping fasteners tight
• Free-spinning devices include toothed and spring
lock washers and screws and bolts with washerlike
heads. The fasteners spin free in the clamping
direction which makes them easy to assemble.
• Prevailing-torque methods make use of increased
friction between the nut and bolt. Metallic types
usually have deformed threads or contoured thread
profiles that jam the threads on assembly.
• Chemical locking is achieved by coating the fastener
with an adhesive.