diameter peg the increased spreading increases the return bias of the fingers and in this manner the clamping forces provided on peg 25 can be increased a further embodiment of the present invention is shown in fig9 and 10 in which a corner portion of a container flange 14 is shown with a circular opening 60 as shown in fig9 opening 60 is located within flange 14 and is not open to peripheral edge 18 as in previous embodiments as shown in fig9 flange 14 has diametrically opposed expansion slots 61 62 located substantially adjacent and concentric to opening 60 separating expansion slots 61 62 from opening 60 are flange portions 63 and 64 respectively when a peg 25 of larger diameter than that of opening 60 is inserted within the opening the opening will deform radially outwardly by moving flange portions 63 64 into the space defining expansion slots 61 62 thus imposing a clamping force on the peg slots 61 62 are shown concentric but need only be concomitant to opening 60 preferably as shown opening 60 is concentric with respect to both the inside arc 66 and the outside arc 67 of slots 61 62 the two expansion slots are within flange 14 in order to allow diametrically opposed expansion of opening 60 however the necessary expansion to obtain the desired clamping force.