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426 Mechanical Engineering Design
Table 8–7

Suggested Procedure for Finding Fastener Stiffness

h
t t t
l t 1 2
l d H
t

d
d

l
L T t
l
l L
T
L l d
L
(a) (b)
Given fastener diameter d and pitch p in mm or number of threads per inch

Washer thickness: t from Table A–32 or A–33
Nut thickness [Fig. (a) only]: H from Table A–31
Grip length:
For Fig. (a): l thickness of all material squeezed
between face of bolt and face of nut
h + t 2 /2, t 2 < d
For Fig. (b): l =
h + d/2, t 2 ≥ d
Fastener length (round up using Table A–17*):
For Fig. (a): L > l + H
For Fig. (b): L > h + 1.5d
Threaded length L T: Inch series:
1

2d + 4 in, L ≤ 6in
L T = 1
2d + in, L > 6in
2
Metric series:
⎧
⎪ 2d + 6mm, L ≤ 125 mm, d ≤ 48 mm
⎨
L T = 2d + 12 mm, 125 < L ≤ 200 mm
⎪
⎩
2d + 25 mm, L > 200 mm
Length of unthreaded portion in grip: l d = L − L T
Length of threaded portion in grip: l t = l − l d
2
Area of unthreaded portion: A d = πd /4
Area of threaded portion: A t from Table 8–1 or 8–2
A d A t E
Fastener stiffness: k b =
A d l t + A t l d
*Bolts and cap screws may not be available in all the preferred lengths listed in Table A–17. Large fasteners may not be available in fractional
inches or in millimeter lengths ending in a nonzero digit. Check with your bolt supplier for availability.