2 things - according to the manual it looks like it calls for shear pins with nylon lock nuts and as far as i can tell everything is std size, not metric. Looking here a grade 8.8 metric bolt is close to grade 5:
https://www.boltdepot.com/fastener-i...ade-chart.aspx
Make sure the shear bolt size is correct; i've seen small ones that slop around break easily and it won't have the strength needed because it's a smaller bolt.
Hope this helps.