Answer:
The material strength is given as 100,000 PSI
To find the tensile load capacity of a threaded rod, we multiply the Strength of the material with the Stress area for the bolt.
A_{t} = 0.7854 (D - \{0.9743}{n})^{2}
Where D is the Basic Major Diameter
n is the Number of threads per inch
At is the Tensile strength area of the bolt.
For 5/16 - 18 UNC thread
D = 0.3125
n = 18
Therefore the tensile load capacity is = 100000 X (0.7854 X (0.3125 - 0.9743/ 18) ^2
= 5243 lb.
Similarly for 5/16 - 24 UNF , only the n value changes to 24
we get the tensile load capacity = 5806.6 lb
Hence the fine thread bolt is stronger because it has more tensile load capacity.
For metric Bolts
We have to consider all values in SI units
Strength = 689 MPa
We get for M8 -1.25
Tensile load capacity as = 689 X 36.6 = 25223 N = 5670 lb
For M8 -1
Tensile load capacity as = 689 X 39.167 = 26986 N = 6067N
Strength of 5/16 - 14 Acme thread
We use the imperial fomula as mentioned above,
The tensile capacity is 4634 lb.
