the first component 10 into the recess 25 is not restricted and furthermore is guided by ramp surface 16 in engagement with ramp portion 24 it should be noted that the distance b between the plastics engagement surface 22 and the further abutment surface 26 is less than the distance c between the abutment surface 20 and barb edge 14 a thus progressive engagement between the first and second components causes the plastics engagement surface to plastically deform around the relatively rigid barb 14 since the distances b and c provide for an interference fit between the first and second components once the first and second components are fully engaged in this case wherein top surface 28 of the first component lies flush with surface 30 of the second component the assembly is left to stand for a predetermined time typically 24 hours during this predetermined time period the plastics material of the plastics engagement surface in the vicinity of the barb edge 14 a is under a stressed condition and tends to relax and creep away from barb edge 14 a some material will creep along the ramp surface 16 and other material will creep behind the retention surface 18 in particular that material that creeps behind the retention surface 18 tends to increase the force required to disengage components in the direction of arrows g with reference to fig2 and 3 there is shown further first and second components 110 and 112 having features labeled 100 greater than those features which perform the same function on first and second components 10 and 12 in this case the abutment surface 120 is in the form of a barb 140 which faces barb.