What grade propeller bolts

Just my opinion;

Class 8.8 is sufficient.

Class 10.9 (the next step up) is overkill

I agree with Sean.

I will order 8.8 then. Thanks for the response. Looks like I can only get 120mm or 130mm long so I will have to get 130 and cut them back as the 130mm length bottoms out on the spacer hub and 120mm measures to barely get through the lug threads in the spacer.

I am at a bit of a dilema with securing them as there isn't a way of safety tying them on the bolt head side due to the design of the Sonex spinner and the back side is blind so can't put a nut there. Saber the spacer manufacturer told me to use loctite 242 but I think it would be difficult to measure torque using that after the first time it sets. Nordloc washers seem to hold exceptionally well as I found when I had to remove my engine mount bolts and was hard to get them to start moving past the Nordloc teeth when I removed those bolts so I am wondering if anyone else has used Nordloc washers for the prop bolts? 

Attached is a picture of the spacer arrangement. The spacer itself can be sucured to the prop flange and double nuts for locking but the spacer lugs are blind against the prop flange. The other picture shows the Sonex spinner and how it doesn't accomodate a space for safety wire

No safety wire necessary. Just use Nord lock washers and Locknuts. They will not come loose. Where I live I rarely see safety wired prop bolts. Almost all have Nord washers and Locknuts. I see Nord lock washers all over now days. 

https://www.amazon.com/s?k=Nord+lockwashers&crid=1QRNKVL9AQPY4&sprefix=nord+lockwashe%2Caps%2C142&ref=nb_sb_noss_2

Lock nuts aren't an option for the prop bolts on this prop spacer, just the Nordlocs is all that can be installed.