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fineness modulus[′fīn·nəs ′mäj·ə·ləs]
A number denoting the fineness of a fine aggregate or other fine material such as sand or paint.
A measure of the fineness of an aggregate; a factor obtained by adding the total percentages of an aggregate sample retained on each of the following sieves and dividing the sum by 100: No. 100 (150 µm), No. 50 (300 µm), No. 30 (600 µm), No. 16 (1.18 mm), No. 8 (2.36 mm), No. 4 (4.75 mm), 3/8 inch (9.5 mm), 3/4 inch (19.0 mm), 1½ inch (38.1 mm).