One is longer than the other

 

Bumper bolts.

 

I concour, bumper or running boards?

 

I'm with Ax on this one. Heads are too big for running boards.

DW

 

But different lengths?

 

Those are rear bumper bolts .Length from under the head please ? They should be 1 5/8 " .What yr. truck are you working on , what yr. are those from or what yr. did they come with ?

 

Some previous owner could have gotten bumper bolts from who knows what..
Pretty common item.

 

Agree with everyone else pumper bolts.

 

Yup, bumper bolts. I'm just guessing here....the shorter bolts are probably for the holes that just go through the bumper and the frame bracket, the longer ones through the bumper, the frame bracket, and an additional support bracket....usually the outer holes.

Bobby

 

I don't think stock bumper bolts were chrome, tho.

 

That depends on what they are off of, or if they are aftermarket.
Most of the cars and trucks from the 60's that I have worked on had chrome bumper bolts.

 

People often changed the bolts to add accessories: front license plate bracket, aux bumper bar, ???