I believe you need M5 x 45 millimeter. I just went and measured my Level 2. I would go to your hardware store and get a M5x 45 and find a washer and nut to fit. The washer goes in the front. It appears to connect in the back with a nut and I don't see a washer. I put it on awhile back and cant remember the exact set up...
Make sure you put loktite. On your pre ride and post ride inspection Make sure to check your fasteners on your fenders.
I use ink pen to mark bolts, makes it easy to check at a glance if they have come loose.
A helpful advice i found here on EBR.