Bolt Shear Strength: 1/4 UNF - Understanding the Difference

[johnfin]

I was looking at bolts strengths on this chart (bottom of page)

http://www.derose.net/steve/resources/engtables/bolts.html#largebolts

and saw that for a 1/4 unf the bolt shear was around 370 but the chart below it listed it at 2700. Why is that?

 

[turbo]

There is a big difference between safe working load and breaking strength, so you should check the numbers that you are comparing to see if they are equivalent.

Those numbers change a lot as you change bolt grades, too. My brother manages a company that makes extruded plastic products, and he routinely has to source grade 8 and grade 9 bolts to mount the extrusion dies to the machinery. Between the high torques and the temperature extremes, these bolts can be very difficult to remove for die-changes, so high-grade bolts are a must. High-grade bolts are very expensive, but not as expensive as the production-loss involved in drilling out stripped bolts, purchasing new heads for the extrusion machines, installing helicoils, and other stop-gap solutions while waiting for new heads to arrive.