Abstract: A bowling ball shaped device having a hollow interior and appropriate cut out wall portions with three receptacles, adjustably mounted therein, with plugs, removably disposed in the respective receptacles, provided with holes fitted to the thumb and two fingers of a bowler. A first adjustment means is provided to laterally adjust the position of the thumb hole receptacle, a second adjustment means pivotally adjusts the thumb hole receptacle toward and away from the finger holes, third and fourth adjustment means, individually pivot the pair of finger hole receptacles toward and away from the thumb hole receptacle, and a fifth adjustment means is individually provided for both of the finger hole and thumb hole receptacles whereby each of said receptacles may be circularly rocked about its inner end and locked in any desired outwardly diverging angular relationship to its normal radial axis. Gauge means is also provided to record said angular relationship.