The invention provides a stabilizer having integral steel blades with preformed apertures into which are cold pressed plugs of hard material, which is characterized in that some of the plugs of hard material inserted into the preformed holes in each blade, each have embedded therein and located exposed at the outer surface thereof, at least one diamond. Advantageously the diamond containing plugs are particularly located so that they are concentrated in those regions of the blade which, when the stabilizer is used in a borehole, are subjected to the greatest wear, viz. towards the leading end of each blade and at sharp changes of contour.