Materials of the Non-magnetic drill collars are from chrome manganese, low carbon alloy obtained by combining a proprietary chemical analysis and a rotary hammer process. The material is resistant to stress corrosion cracking, with high machine ability and no tendency to galling. magnetic permeability (when MPS=1 105/4 Nm) relative max:1.010 average: Ur >=1.005 magnetic field gradient (hot spots) max: B 0.05micro tesla/100mm The non-magnetic drill collars exhibit the mechanical properties indicated below along their entire length. The table is derived from test samples of steel taken from a point 1?below the surface.