Abstract: An adjustable aid kit having a thumb sleeve and a pair of finger sleeves of hollow cylindrical form which are placed within the recesses of the bowling ball. Thumb and finger inserts are provided and fit coaxially within the sleeves. The thumb and finger inserts each have a reduced diameter threaded head which is received in a threaded aperture provided in the internal end wall of the sleeves to lock the inserts in the sleeves. The inserts each possess particularly shaped thumb and finger passages which, when employed by the thumb and fingers of the bowler on certain angles, cause particular force vectors to be applied to the bowling ball as the ball is released from the bowler's hand.