Patent ID: 8808110

Claim:
A multi-piece solid golf ball comprising a solid core encased by a cover of one or more layer, which solid core has an inner core layer and an outer core layer, wherein the inner core layer is formed primarily of a thermoplastic resin, has a diameter of from 21 to 38 mm, has a JIS-C cross-sectional hardness of from 60 to 83 at any single point on a cross-section obtained by cutting the inner core layer in half, and has a cross-sectional hardness difference between any two points on the cross-section of within ±5; the outer core layer is formed of a rubber composition made primarily of polybutadiene rubber; the core of the inner core layer and the outer core layer combined has a diameter of from 35 to 42 mm; and, letting (b) represent the JIS-C cross-sectional hardness of the inner core layer 1 mm inside a boundary between the inner core layer and the outer core layer, (c) represent the JIS-C cross-sectional hardness of the outer core layer 1 mm outside the boundary, and (d) represent the JIS-C surface hardness of the outer core layer, the value (c)-(b) is in a range of from −15 to 0 and the value (d)-(b) is in a range of from −10 to 20 , and the specific gravity of the inner core layer is from 0.8 to 1.4 and the specific gravity of the outer core layer is from 1.0 to 3.0.