Abstract: A bowling ball thumb insert including a generally planar plug having an upper surface, a lower surface, a peripheral edge interconnecting the surfaces and thereby defining a thickness, and a bore disposed therethrough and with the plug positionable within a thumb hole of a bowling ball; a plurality of sleeves with each sleeve having a circular planar bottom wall with an interior top surface, an exterior bottom surface, a peripheral edge extended between the surfaces, a bore disposed therethrough, and a tubular side wall having a characteristic thickness, an upper end, and a lower end with the lower end coupled with the interior surface of the bottom wall; and a bolt extended through the bore of a sleeve and the bore of the plug, the bolt further projected outwards from the lower surface of the plug for threaded securement to a complimentary threaded bore formed at a bottom end of a thumb hole of a bowling ball.