Tolerances for size.

(a) When a range is specified as, for example, “ 18/20 ,” no tolerance for counts above or below the range shall be allowed. (b) When the minimum, or minimum and maximum diameter are specified, a total tolerance of not more than 10 percent, by weight, may fail to meet the specified size requirements: Provided, that not more than one-half of this amount, or 5 percent, may be below the minimum size specified.