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If you're not measuring, you're guessing. At the bare minimum, a good dial caliper and some Plastigauge will get you in the ballpark. A 0- to 1-inch micrometer is good for wristpins and valve stems, a 1- to 2-inch mic is good for small crankshaft journals, a 2 to 3-inch mic for just about all other crankshafts, a 3- to 4-inch mic for smaller pistons, and a 4- to 5-inch mic for most big- and small-block pistons. A 12-inch dial caliper is good for measuring pushrods and the expanding calipers are great for checking cylinder head runner dimensions.