Abstract: An insert that can be installed in a finger or thumb hole in a bowling ball after the existing hole has been enlarged includes a cylindrical tube of a resilient material. The space inside the tube is divided by a plenum and one end of the tube is closed by a plug to form a chamber within the tube between the plenum and the plug. A ballast material is included in this chamber to compensate for the weight of the ball material removed when the hole was enlarged to accommodate the insert, thereby bringing the ball back into balance. The insert is bonded into the enlarged hole with the chamber at the bottom of the hole. The resilient material of the tube provides a more comfortable grip on the ball. In the preferred embodiment, the plenum and the tube are a unitary structure.