The tube is about 10-feet long. We used 1-1/2-inch ABS pipe, schedule 40. The inside diameter of this pipe is about 41 mm. Since the diameter of a ping-pong ball is about 38 mm, this leaves a little over 1 mm clearance for the ping-pong ball in the tube. read more
The ball used in table tennis has a diameter of d = 40 mm. Some time ago it was 38 mm. 40mm=4cm, 4cm/(2.54cm/in)=1.575 (rounded) inches. read more
The current standard ping pong diameter is 40mm or about 1.58 inches. Formerly they were 38mm which is about 1.49 inches. As always, divide the number of millimeters by 25.4 to get inches. read more