Abstract: This fastening device, notably for fixing an object to a hollow partition or wall, comprises a splined plug, a screw and a nut; the bottom of the gaps formed between the splines is provided with a slit, except at the plug ends, to enable the splines to separate and expand when contracted as a consequence of the tightening of the nut by means of the screw; the nut carries lugs corresponding to the gaps formed between the plug splines so that when the device is tightened home the lugs registering with the gaps engages the latter to assist in reinforcing the locking action exerted by the expanded and twisted splines against the inner face of the partition.