These drilled balls are excellent for use as pendulum bobs or in impact and collision experiments. All drilled balls feature 3mm countersunk holes so pendulum cord knots can be recessed. Additional Info: These drilled balls are excellent for use as pendulum bobs or in impact and collision experiments. All drilled balls feature 3mm countersunk holes so pendulum cord knots can be recessed. Package Size(L x W x H): 0.75 X 0.75 X 0.75 (IN) Categories: Mechanics, Pendulum Balls HTS Code: 9023.00.0000 UNSPSC: 6.01e+007 Country Of Origin: INDIA