Bowling balls without finger holes are intended to be held in the palm, meaning they are usually much lighter than a typical tenpin ball. Such balls might be used in some of the more common pin bowling variations, including duckpin and candlepin. Balls with finger holes are denser and heavier. This ball looks to be reinforced with metal, perhaps an effort to repair damage.
( C ) Copyright 2018 IBMHOF (photo by Heritage Werks)