A bowling ball insert, comprising:
- an outer sleeve comprising a cylindrical wall having an inner surface defining an inner circumference and an inside diameter, and an outer surface defining an outer circumference and an outside diameter, the distance between the outer surface and the inner surface defining an outer sleeve wall thickness, said wall having an upper end and a lower end,
- said outer sleeve further having an upper lip at the upper end extending outward from the inner surface for a distance greater than the distance of the outer wall thickness,
- said outer sleeve further having a floor at the lower end extending inward from the cylindrical wall around the circumference of the wall, said floor being open at its center to provide an outer sleeve floor opening having a diameter at least one-half the inside diameter of the outer sleeve, said outer sleeve floor having a floor thickness,
- wherein the inner surface of the outer sleeve wall comprises a first vertical channel that is open at the top and with a depth less than the thickness of the sleeve wall and with a first channel width, and a second vertical channel that is open at the top and with a depth less than the thickness of the sleeve wall and with a second channel width differing from said first channel width,
- wherein the inner surface of the outer sleeve wall comprises a first horizontal channel having a first end open to the first vertical channel and a second end that is closed, and a second horizontal channel having a first end open to the second vertical channel and a second end that is closed;
- and an inner sleeve comprising a cylindrical wall having an inner surface defining an inner circumference and an inside diameter, and an outer surface defining an outer circumference and an outside diameter, the distance between the outer surface and the inner surface defining an inner sleeve wall thickness, said inner sleeve having an upper end and a lower end,
- said inner sleeve further having a floor at the lower end extending inward from the cylindrical wall around the circumference of the wall, said floor being open at its center to provide an inner sleeve floor opening having a diameter less than the diameter of the outer sleeve floor opening,
- wherein said inner sleeve receives a slug material that is configured to be drilled to provide a substantially custom fit for a finger or a thumb of a user,
- said inner sleeve further having a first tab having a width sized to fit in the first vertical channel and the first horizontal channel, and a second tab having a width sized to fit in the second vertical channel and the second horizontal channel, but not in the first vertical channel, wherein said first tab and said second tab are spaced around the circumference of the inner sleeve such that when the first tab is aligned with the first vertical channel the second tab will be aligned with the second channel.