Diamond Reaming Shell is connected to a core bit. While the drilling is done by the bit, grinding of side surface can be done simultaneously. The outside surface of the reamer shell is inset with diamonds to maintain the gage of the hole as the O.D. of the core bit wears. Diamond reamer shell is used to prevent early wear and tear of the outer diameter of the Bit, and is also used to prevent vibration and deformation of the hole walls. Having a cylindrical shape, with diamond particles attached at outside diameter. The diameter of the reaming shell is made bigger than that of a bit.