Regulation 50
In the case of weights of the flat-circular type made of iron, the lead inserted for adjustment shall be not less than one-eighth of an inch in thickness; the approximate depth of the adjusting hole shall be equal to three-fifths of the centre thickness of the weight; and the approximate minimum distance of the lead from the surface of the weight shall, when new, be one-fifth of the centre thickness of the weight.
The adjusting holes in such weights shall be circular and their smallest diameter shall be approximately—
in the case of weights of a purported value of 4 pounds or 2 pounds, 1 inch;
in the case of weights of a purported value of 1 pound, three-quarters of an inch;
in the case of weights of a purported value of 8 ounces or 4 ounces, half an inch.