Thjs is a 2 stroke, 4 cylinder Merc 500 crank.  Large taper, thick top cheek, single row needle bearings, 28 count.  It is in excellent condition, has been polished.  This style crank was used in 50hp Merc 500's from 1969 to 1974.  Does not fit 1975 UP blocks.  Flywheel nut is used, just there to protect the threads.