Mounting Bolt Confusion Go Rhino Running Boards

[sgnden]

2021 GMC 2500 Crew Cab.  The RB20 bolt selection coupled with semi-worthless instruction sheet has me wondering which of the bolts are supposed to be used for attaching the boards to the brackets.  

 

They included zinc coated bolts with washers that I used to attach the mounts to the frame but they supply TWO different types for the board to be mounted to the bracket. One is a typical M8 1.25x25mm w/ flat washer and lock washer and one is similar but has a TAPER and pre-installed large washer (no lock washers).  The tapered one has a slightly finer tooth and does go into the mounts very smoothly while the M8 is tighter.  If I can't get an answer, I'll just go with the tapered bolt but I'd prefer to do it per spec...if there was any info out there that I could find. So far nothing.

 

Picture attached. Please pardon the crap quality but you'll get the idea.

 

Thanks! 

Edited January 3, 2021 by sgnden