Thread Calculations - Polycrew.com

1 Caution: All information in Polycrew Articles is advisory only and the use of this information is voluntary. Polycrew has made a determined effort to present the contents accurately. Document ID: 2016110601 Date: 1/8/2017 p. 1 of 2 Thread Calculations 1. These equations originate from ASME and ISO specifications for inch and metric threads, respectively, as well as materials and mechanical engineering concepts. Inch Threads Metric Threads References ASME ISO 68-1 ISO 724 ISO 898-1 Tensile stress area of threads, As = 2= 4 ( )2= 4( 2+ 32)2 1= 118 2= 34 3= 1 8= 3 34 1 = 32 = 32 1 = 4( 9 316 1 )2 d1 = minor diameter of external Thread d2 = pitch diameter of external Thread d3 = minor diameter of external Thread H = height of fundamental triangle d = nominal diameter of fastener, in n = threads per inch, in As = tensile stress area of threads, in = 2= 4 ( )2= 4( 2+ 32)2 1= 54 2= 34 3= 1 6= 17 324 = 32 = 4( 13 324 )

2 2 d1 = minor diameter of external Thread d2 = pitch diameter of external Thread d3 = minor diameter of external Thread H = height of fundamental triangle d = nominal diameter of fastener, mm P = pitch, mm As = tensile stress area of threads, mm Single shear stress area of threads, An = 2= 4 32 3= 3 34 1 = 4( 3 34 1 )2 d3 = minor diameter of external Thread d = nominal diameter of fastener, in n = threads per inch, in An = single shear stress area of threads, in = 2= 4 32 3= 17 324 = 4( 17 324 )2 d3 = minor diameter of external Thread d = nominal diameter of fastener, mm P = pitch, mm An = single shear stress area of threads, mm Basic torque-tension relationship of threaded fasteners = = torque, in-lb K = nut factor, unitless D = nominal diameter of fastener, in F = clamp load, lbs = = torque, N-mm K = nut factor, unitless D = nominal diameter of fastener, mm F = clamp load, N Caution: All information in Polycrew Articles is advisory only and the use of this information is voluntary.

3 Polycrew has made a determined effort to present the contents accurately. Document ID: 2016110601 Date: 1/8/2017 p. 2 of 2 Change in length of bolt due to applied load = = NOTE: likely Aj >> Ab bi = length of bolt due to F F = clamp load ( applied load) Lbi = initial bolt length before F Eb = elastic modulus of bolt material Ab = tensile stress area of bolt Lji = initial joint length before F Ej = elastic modulus of joint material Aj = compression barrel area of joint material Change in joint force due to change in temperature = ( )( + ) NOTE: positive F increases tensile load on bolt (aka increases clamp load on joint) while a negative F decreases the tensile load on the bolt (aka decreases the clamp load on the joint).

4 F = change in force T = change in temperature j = CTE of joint material b = CTE of bolt material Ej = elastic modulus of joint material Aj = compression barrel area of joint material Eb = elastic modulus of bolt material Ab = stress area of bolt Respectfully, Tyler Olson Fastener Enthusiast Polycrew Contributor