They are studs which screw into the hub. I have found normally the threads in the nut strip before the stud shears.
The nuts are M10 x 1.25. You can find stainless flanged nuts on ebay cheaper than Yamaha items, no rust either http://www.ebay.co.uk/itm/M10-X-1-25-STAINLESS-STEEL-FLANGE-NUTS-FINE-THREAD-PITCH-10mm-x-1-25mm-serrated-/231828370889?var=531071993189&hash=item35fa0c35c9:m:mdAcE1IULzJkpSMiHKEwZow
Their serrated so when you torque them up they'll bite into your sprocket. You could use thread lock but they should stay put.
I'll always swap for stainless, cheaper than standard and no worries about rusty nuts