Pool balls: size, weight and materials.

The regulation pool ball

The WPA specification sets pool balls at 2.25 in in diameter, plus or minus 0.005 in, and 5.5 to 6 oz in weight. The BCA reproduction gives the same numbers. Converted to grams, the sources differ slightly: the WPA reproduction gives 156 to 170 g, while Wikipedia gives 160 to 170 g.

Manufacturers can hold tighter limits than the rulebook. Aramith's own specification for its 2.25 in balls is plus or minus 0.003 in on diameter, with roundness within 0.002 in (0.0012 in on its top grade). It lists resin density of 1.69 to 1.87 depending on the resin, and hardness above 73 HRH (above 80 HRH for Super Aramith Pro).

Trick Shot Tim's point is why that matters: tighter roundness, diameter and weight tolerances make balls roll truer and make replacements easier to match.

In a pool set, balls 1 through 7 are solids, 9 through 15 are stripes, and the 8 belongs to neither group. Wikipedia dates striped balls to around 1889.

Phenolic resin vs polyester

Black Label Billiards describes phenolic resin as a thermoset made from phenol and formaldehyde under heat and pressure, which cannot be remelted once molded. Aramith balls are 100% phenolic resin. Polyester is the budget material: Black Label says polyester balls are softer, lose their shine and roundness faster, chip more easily, run hotter from friction, and leave burn marks on the cloth.

Aramith makes strong durability claims for its balls. These are the manufacturer's claims, and no independent testing is cited for them:

• More than 4,000,000 impacts, resistance to 250 °C (482 °F) friction temperatures on the break, and up to 5 times the life of other balls.
• 50 times more impacts than polyester balls.
• Its Duramith treatment extends ball life by up to 50%, with less cloth wear and fewer burn spots.

Another quality marker from Trick Shot Tim: cheaper balls may have painted or inlaid numbers that wear or fall out, while better balls have precision-engraved numbers.

For background, Wikipedia traces ball materials from wood and clay through ivory (favored from at least 1627), celluloid composites (Hyatt's 1869 patent), Bakelite, acrylic, and today's phenolic resin and polyester. The equipment history page covers that story.

Cue ball variants

Measles cue balls

Aramith's Pro Cup "measles" cue ball carries six red dots so players and viewers can see spin. A black-dot version came out of a collaboration with Matchroom and was used at the Mosconi Cup; it is 2.25 in and about 6 oz. Marked cue balls are also a practice tool, because they show what spin you actually put on the ball. See cue ball control.

Coin-op cue balls

Coin-operated tables have to separate the cue ball from the object balls. Some use a cue ball that is larger and slightly heavier than standard, which Trick Shot Tim and Wikipedia note makes draw harder to apply. Others use a magnetic cue ball with an embedded metal layer, or sense the more translucent cue ball optically. Trick Shot Tim warns that a low-quality magnetic cue ball can wobble. Diamond says its Smart coin-op table uses a regular phenolic cue ball with no magnet.

TV ball sets

TV sets change some colors so the balls are easier to tell apart on television. Wikipedia says pink replaces the dark purple of the 4 and 12, and a lighter brown replaces the maroon of the 7 and 15, and some sets add a spotted cue ball. The Aramith Tournament Pro Cup TV set follows that pattern, with pink 4 and 12, brown 7 and 15, and a six-red-dot cue ball.

Snooker, carom and other sizes

European carom rules allow no more than 0.25 mm of diameter variation and 2 g of weight variation within a set, which is either two whites and a red, or white, yellow and red.

Cleaning and polishing

Aramith's instructions for its own products (Monarch Billiards also passes on Aramith's advice to clean phenolic balls after each game):

1. Clean phenolic balls after each game with Aramith Ball Cleaner: shake the bottle, apply with a microfiber cloth, and rub.
2. Buff dry by hand or with an electric buffer.
3. For very hard spots, apply a drop of Aramith Ball Restorer, rub, follow with the cleaner, then buff.

Aramith says both liquids are silicone free. Its microfiber cloth can be washed at 60 °C (140 °F) but should not be ironed. We found no source covering ball-cleaning machines, so we do not describe them.