There are several bolts already on the car that can be exchanged for a smaller bolt, ie the bolt from the under bonnet fuse box to the slam panel, the bolt from the plastic strap holding the A/C pipe & bolt holding the coolant tank, amongst others if you look over the engine
you can also use new 16mm X 6mm with a 10mm head in each engine cover hole.
Remember the bolts that fits into the cam cover which spits out the oil is directly over the chain so must not be to long in the first place.