Dictionary.net

• Balls placed under a heavy object to reduce the friction, while that object is moving horizontally. Some forms of swing-bridges have such balls placed under them.

1899 - The american dictionary of the english language.
By Daniel Lyons

• A mechanical contrivance for moving heavy weights round a centre, as in cutting a block of marble.

1914 - Nuttall's Standard dictionary of the English language
By Nuttall, P.Austin.