Are 2 zinc 3/4 bolts strong enough to hold ICC/DOT bumper/tube?

Have you considered "Duck Tape"?

 

pretty accurate but ...

1 - the coatings on the bolt have nothing to do with the strength of the bolt. Be it zinc-plated, zinc-coated, cold galvanized or hot galvanized coating, the coating won't diminish the tensile strength or diminish the shear strength.

2 - Anodizing is a process of sealing aluminum surfaces. You are thinking about what is commonly called the Blacking or black oxidizing process.

That said the ICC bumper and its components are to withstand a 20,000 lb force. Given that many of these bumpers use a minimum of four bolts to hold it onto the frame/body of the truck, Grade 2 bolts can be used, Grade 5 is better, and of course, Grade 8 is the best. Failure of the bumper, and the doubt that any of the inspection officers have any clear knowledge of what the differences are, I would say you are safe in using grade 2 bolts.

 

Cadmium plating^. I think he might have been referring to cadmium plated bolts.

 

No cadmium plating is different process and it leaves the bolt silvery coating on them.

blackening is when the bolt has a chemically oxidized surface. If done incorrectly, it can lead to weakening of any surface treatments to strengthen the fasenter.

 

I believe your speaking of phos and acid finished bolts... Very corrosion resistant under most any natural weather conditions.

 

Yes, but zinc-plated bolts are often just plain old 'mild' steel, which has enough strength when new, but not after corroding for a few years..

Actually, there has been a big industry-wide program to REMOVE cadmium from plating; anything that is RoHS-compliant is cadmium-free. Only parts with a specific callout for certain military platings use cadmium at all anymore. This has all changed in the last 20 years.

 

Grade 8s are what you're looking, I don't buy anything else other than a few smaller stainless bolts for doodads.

 

My Lowe's has grade 8 bolts, but they're in the special drawers at the end of the bolt isle not with the rest of the bulk fasteners. Not sure I have ever needed something as big as 3/4, but I have bought 1/2 in grade 8s there before.