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Fasteners and Power Screws

Bolt Preload and Torque

Shigley's bolted-joint method for a preloaded tension joint: the tensile-stress area and proof load of a Unified or ISO thread from the standard tables, the preload as a fraction of the proof load or entered, the tightening torque by the nut factor T = K F d and by the thread-and-collar friction equation with its pitch, thread-friction and underhead-friction parts, the preload scatter of the tightening method, the bolt stiffness from its threaded and unthreaded lengths in the grip, the member stiffness by Shigley's conical frusta through every layer of the grip (plates of different materials, a washer, a gasket; cap screws in a tapped hole by the effective-grip rule) and by the Wileman exponential fit, the joint constant, the bolt and member forces under the external load, the separation load and factor, the proof-load and overload factors, the number of bolts for a required load factor, and for a fluctuating load the Goodman, Gerber and ASME-elliptic fatigue factors with the rolled-thread endurance strengths. Default: Shigley's Example 8-4 (six 5/8 in-11 UNC grade 5 bolts in a cast-iron pressure-vessel flange under 36 kip).

1 worked example reproduced, listed on the tool page.

Thread Engagement and Strength

Strength of a threaded joint from the public-domain NBS Handbook H28 (Screw-Thread Standards for Federal Services, 1969): the basic profile and the tensile stress area of a Unified (UNC, UNF, UNEF, classes 1A-3A / 1B-3B) or ISO metric thread chosen from the standard series or entered, the limits of size from the H28 allowance and tolerance formulas with the substituted numbers, the thread shear areas of the external and internal threads over the length of engagement, the tensile strength of the bolt and the stripping strengths of both threads with a check that the bolt breaks before either thread strips, the required length of engagement (equal strengths, the H28 shear-area rule and the J correction for a weaker nut or tapped material), a proof-load check and the nut-factor torque, margins against an applied load, and an optional threaded insert as a second engagement in a parent material. Default: a 1/2-13 UNC-2A steel bolt (120 ksi) in a 2B nut of the same strength engaged over 0.5 in.

1 worked example reproduced, listed on the tool page.

Other Mechanical Design sections

Shafts · Gears · Bearings · Springs · Pressure Vessels · Tolerances · Mass Properties · Vibration · Acoustics · Brakes, Clutches and Belts · Machining and Manufacturing · Lubrication and Wear