40mm Table Tennis Balls

In part one we looked at the different types of balls.

Let's now take a look at what qualities are needed by a table tennis ball to make it onto the ITTF approved list.

The ball must be white or orange, and matt, and must appear to be uniform and only have one seam.

Although the official rules state that the ball shall be 2.7g, any weight between 2.67g and 2.77g is acceptable for any one ball in the test batch.

No more than 1 ball out of the 24 tested may be outside this range and the sample mean must be between 2.69g and 2.76g.

The minimum diameter of every ball must be at least 39.50mm, and its maximum diameter must not exceed 40.50mm.

The sample mean average diameter, i.e. the mean of the average of the maximum and minimum diameters for each ball, must be in the range 39.6mm to 40.4mm.

The sphericity of a ball - or more correctly the lack of sphericity - is the absolute difference between its minimum and maximum diameters.

The sphericity of any ball must be less than 0.35mm, and the sample mean sphericity must be less than 0.25mm.

Veer is a measure of the total sphericity of the ball.

It's measured by rolling the ball down a slight incline onto a horizontal surface, and measuring the distance by which it deviates from a straight line as it rolls across the surface.

Balls shall not deviate by more than 175mm from the center-line.

Every ball must rebound to a height of not less than 240mm or more than 260mm when dropped from a height of 305mm on to a standard steel block.

Hardness is measured with a fully automated and computerised tester. A 20mm diameter pin presses against a pole of the ball.

Measurements are made on each pole and the average for the poles provides a measure of the hardness.

The coefficient of variation shall be not greater than 0.06mm.

The stamp on the ball must include the following four components:

• The ITTF Approval. This may be indicated by the initials ITTF or ITTFA, or by the words "ITTF approved", or by using the ITTF logo
  
  
• the trademark or brand name
  
  
• the inscription "40" or "40mm"
  
  
• the name of the country where the company headquarters are registered, or the expression "made in ..."

No other text is permitted.

For more information, tips and recommendations about table tennis equipment, take a look at my other articles ...