The X series uses a 3/4 socket. You need to use a torque wrench and not tighten them any tighter than 55-60 lbs. Exmark uses a spline bushing to keep the blade from self tightening when it hit's something or during mowing. Definitely do not use an impact wrench on an Exmark if it has the spline bushing. All it takes is one hand to hold the blade and they come off very easily with a ratchet. There should be a warning sticker on the deck that tells you the amount of torque to use. Also use copper based anti-seize on bolts.
This is assuming they are the same as the X series.
Exmark Lazer Z X series
Scag Turf Tigers W/Briggs Vanguards Velocity decks,
My friend Mark says: "The secret to a good cut is never looking back!" .