Same happened here,
I didn’t see or understand the difference M5 screw of M8 bolt.
Apparently everything above M5 is considered a bolt and under is a screw?
Or does the cross head pan head make it a screw?
Here in the Netherlands we call everything with metric thread “bout” (bolt).
So i came home with M5 hex heads which didn’t fit, changed them out for M5 allen head at work.
They fit fine except tensioning the M8 besides the steppers a little bit difficult.
Oh and sidenote: the primo was much easier to assemble than the burly was, big steps were made!
The nut traps being the right size for metric nuts was so much easier