Aluminum running boards hardware help?

I am trying to install aluminum running boards but the hardware included (13mm bolts) don’t seem to want to go into the body? Is 13mm is used on the oval step bars ? I am using the right mounting holes but each bolt only wants to go halfway, if that?

 

I encountered the same problem. I cleaned out the hole and sprayed some wd-40. Make sure you have the correct thread and length.

 

What’s the correct thread and length? I’m hoping rust isnt an issue also.

 

I can check when I get home, I have a box of these bolts and nuts.

 

Found this will try to source similar size ones tomorrow

http://toyotaparts.sparkstoyota.com/install/PT767-35190inst.pdf

 

M8x1.25 is the thread size I believe