4287. The most common standard size of bubble caps used in industrial operation is September 7, 2025 by Admin 1″ dia cap with 0.5″ dia riser. 6″ dia cap with 4″ dia riser. 8″ dia cap with 1″ dia riser. 4″ dia cap with 8″ dia riser. ✅ The correct answer is option B.