Zeusimo

I Don't Have That Size Socket... Gotta Buy One

I think its just 19mm, but in case you were wondering, hardware store bolts wont have the right shoulder diameter/metal strength and WILL fail. Resulting in removed legs, and chunks of your car... Just FYI =)

ARP has the bolts you need. OR NOS bolts here http://www.ebay.com/itm/Genuine-Datsun-Flywheel-Bolt-Set-240Z-280Z-280ZX-NEW-/310354337314?pt=Vintage_Car_Truck_Parts_Accessories&vxp=mtr&hash=item48428f5e22#ht_2360wt_1163