James Duff U bolt size

[Got4wd]

Got some heavy duty u bolts from Duffs. Says 9/16. What I’m getting from Duffs is you measure from the threads? I’ve never heard of that before. Am I wrong?

 

[jamesroney]

Got some heavy duty u bolts from Duffs. Says 9/16. What I’m getting from Duffs is you measure from the threads? I’ve never heard of that before. Am I wrong?h

Yes, you are both wrong.

It's very much like buying lumber. You can't measure a 2x4 and get 2 inches.

In general, the u-bolt is specified by its "nominal" thread diameter. Given that 9/16 is .562 inch...I doubt that you would ever be able to measure .562 on the actual hardware.

The root diameter of a nominal 9/16 UNF thread is .502, so any bolt diameter bigger than .502 is as strong as the threaded part. Once you get into the hoop section, I've seen formed strap style u-bolts with flattened out with significantly reduced cross section.

The "minimum major diameter" for a Class 2A UNF is .552. and for Class 3A, it's .550 Your calipers are reporting .548. it is .004 undersized. It is no coincidence that the nominal diameter of a 14mm thread is .551. This happens when you contract a Chinese sub-contractor to build to an SAE equivalent. You end up with "Almost-same" It's also called "Chinese-same" Which is: "Exactly the same, but a little bit different."

I'm starting to see the same thing now with US supplied hardware. The vast majority of hardware is metric, and so the equipment and raw materials are "metric-centric" This is how you end up with 1/4-20 bolts with 10mm heads.

Turns out that Duff is wrong too...but he's a lot more right than you. That's a 9/16 U-bolt.