A stabilizer for a drilling string comprises a one-piece metal loop (1), stabilizing blades (3), and tightening bolts co-operating with internally threaded bores (9) to draw the end portions (4) and (10) of the loop towards each other. The end portion (4) is formed with an involute camming surface (7) on which the end portion (10) rides to urge the end portion (4) resiliently inwards.
