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13. A lot of people like to brag about running a 4-inch Merc crank. The way to distinguish a 3 3/4-inch Ford from the larger Merc (and possibly dispel someone’s bragging rights!) is by the size of the oil plug—on the 8BA crank it’s the size of a pencil; the more desirable Mercury crank oil plug is the size of a finger (to be safe, though, always measure—the standard crank size is 2.138/2.139 on the rod journals and 2.498/2.499 on the mains).