This is the stock bolt used for the crank pulley on the 3000GT/Stealth. It can be used for the stock pulley (dampener) or any of the aftermarket pulleys available.
This sometimes needs replacing because it can get split. It is a special head bolt that allows the use of a 22mm socket around the outside (highly recommended) or just a 1/2-inch driver on the inside of it (NOT recommended). The problem is if you use a 1/2-inch driver on the inside of it, the bolt head can split apart and fail - this is pretty much the single tightest bolt on the car. Due to the fact that they can split, we recommend you check yours and replace it if it is split - of course, we recommend you replace it when you are pulling off the crank pulley for a 60k service or to install a new pulley, rather than replacing it just to replace it. ;-)
NOTE: Mitsubishi apparently became aware of the splitting bolt issue as the new bolts do NOT have the 1/2-inch driver opening on the end.
Select bolt and washer separately.