─────────┬─────────────────────────────────────────┬─────────────────── Maximum │ Circular Openings, Inches │ Passing Screen Size of │ │ Having Circular Aggregate│ │Openings ¼ Inch in Inches │ │diameter, not more │ │ than ─────────┼───┬───┬───┬─────┬─────┬─────┬─────┬─────┼─────────────────── │ 3 │2½ │ 2 │ 1½ │ 1¼ │ 1 │ ¾ │ ½ │ ─────────┼───┼───┼───┼─────┼─────┼─────┼─────┼─────┼─────────────────── 3 │100│ │ │40–75│ │ │ │ │ 15 per cent 2½ │ │100│ │ │40–75│ │ │ │ 15 per cent 2 │ │ │100│ │ │40–75│ │ │ 15 per cent 1½ │ │ │ │ 100 │ │ │40–75│ │ 15 per cent 1¼ │ │ │ │ │ 100 │ │ │35–70│ 15 per cent 1 │ │ │ │ │ │ 100 │ │40–75│ 15 per cent ¾ │ │ │ │ │ │ │ 100 │ │ 15 per cent ─────────┴───┴───┴───┴─────┴─────┴─────┴─────┴─────┴─────────────────── The manufacture of small size cement pipe requires relatively more skill than equipment. As a result great care must be observed in the inspection of cement pipe and in the enforcement of specifications. For large size concrete pipe and reinforced concrete pipe the difficulty of holding the pipe together during transportation and lowering into the trench aid in insuring a good product.