MSP Babowlers
Regulation gives you a range, not a single ball: 4.75-5.00 in across, 3 lb 6 oz to 3 lb 12 oz, drilled for your delivery.
Start with diameter. A regulation duckpin ball measures 4.75-5.00 in (12.1-12.7 cm) across - small enough to palm, which is the point of the game. Stay inside that band; the specification exists so the ball can pass between standing pins rather than over them.
Then weight. The legal range runs 3 lb 6 oz to 3 lb 12 oz (1.56-1.74 kg) - a spread of only 6 oz, so the choice is about control, not power. The lane is still 60 ft (18.29 m) from foul line to head pin, the same as tenpin, and the ball has to carry that full distance without the mass a tenpin ball relies on.
On narrow screens, swipe or scroll the plate sideways.
Grip is the third decision. Duckpin balls are drilled for two-handed deliveries as a matter of course, commonly with three or four finger holes rather than the three-hole tenpin layout. One-handed palmed deliveries and two-handed styles both fit inside the same ball spec; the drilling is what changes.
Clearance is why the spec matters. With pins spaced 18 in apart across the row and a ball no more than 5 in wide, the ball covers barely a quarter of the gap between pin positions. That open space is what leaves the 7-10 and 1-3 standing so often - and what a well-fitted ball helps you use on spare shots.
A practical check before you commit: the ball should sit in your hand without strain anywhere in the 3 lb 6 oz to 3 lb 12 oz window, the finger holes should match a three- or four-finger layout, and the fit should hold up for three balls a frame across a three-hour league night. For what happens on the sheet once you throw it, see How to Score Duckpin Bowling Frame by Frame; for the full measurement table, see Duckpin vs Tenpin: Lane, Pins, Ball and Rules Compared.
Further reading