Product Description The Turbo Grip Fitter helps bowlers find the perfect fit between the 19 sizes available in the Quad Insert line.Size Increments are 1/64″- Standard O.D. of 31/32″-for sizes 19/32″ thru 13/16″- Larger O.D. of 53/64″-for sizes 29/32″ thru 1-1/32″The Quad Classic is a versatile, multifunctional insert that combines a loftier 1/4″ forward pitch on one side and our popular Perfect Oval insert on the other.