because the two examples of a fastening clip in accordance with the invention shown in the drawings are identical to one another with the exception of minor differences , identical references have been used for identical parts and the mode of operation of the clip has been explained only once . in the figures , a fastening clip 1 or 1 &# 39 ; in a known manner exhibits a flat , disc - shaped retainer head 2 extending perpendicularly to the clip axis , a central circular neck 3 having a length corresponding to the thickness of a trim element 4 or the like and a thin disc - shaped sealing collar 5 extending parallel to the retainer head 6 . the sealing collar 5 is followed by a central , rectangular shank 6 connected through a deliberate frangible point 7 to a supporting disc 8 of part circular shape . formed on the underside of the supporting disc 8 are two fastening clip arms 9 of substantially rectangular cross section that extend parallel to the clip axis and away from the supporting disc 8 , these arms being designed to be inclined when the clip is in operative position . the other ends of the clip arms 9 are articulated through respective integral hinges 10 in each case to spreader arm 11 of rectangular cross section extending substantially parallel to the clip axis back to the supporting disc 8 . the other ends of the spreader arms 11 are articulated through integral hinges 12 to that end of the shank 6 which extends beyond the deliberate frangible point 7 . the rectangular shank 6 is provided at the top of its transverse sides with detent grooves 13 adapted to cooperate with the break edges 17 , these being designed as detent edges , of the deliberate frangible point 7 in the following fashion : the fastening clip 1 is inserted into an opening in the trim element 4 in an conventional manner . the trim element 4 ( or to put it more generally , an upholstered covering element ) with a number of fixing clips 1 in position in it is now offered up to a body panel 14 which is to be covered . the clip arms 9 , because of their dimensions , are readily insertable even into a locating hole 15 of minimum size until the supporting disc 8 comes up against the body panel 14 . through an ensuing knock or application of pressure with the heel of the hand to the trim element in the neighborhood of the individual fastening clips 1 , this in a manner conventionally employed when assembling these elements , the deliberate frangible point 7 is ruptured and the shank 6 is driven through the disc elastically deforming the detent edges 17 formed at the resultant opening 16 . this causes the spreader arms 11 to spread apart so that the latter because of their articulating attachment to the clip arm 9 incline the latter outwardly forming detent shoulders causing the supporting disc 8 to be firmly clamped against the perimeter of the locating hole 15 in the body panel 14 . at the end of the inward motion of the shank 6 , the detent edges 17 engage in the detent grooves 13 in the transverse sides of the shanks 6 and thus retain the fastening clip in its assembled position . the engaging , securing and disengaging force required in the case of the fastening clip in accordance with the invention is thus influenced by parameters which the designer can arbitrarily vary by corresponding dimensioning of the detent edges 17 and the detent grooves 13 . the dimensions can be kept within tight tolerances because of the way in which the retention clip is manufactured by injection moulding . the fastening clip in accordance with the invention can thus reliably be so designed that a desired retaining force is reliably and uniformly achieved . the further embodiment of a fastening clip 1 &# 39 ; in accordance with the invention shown in fig3 and 4 has substantially the same construction as that shown in fig1 and 2 . the sole distinction resides in the provision of an extension 18 on the shank 6 . the extension has a conical guidehead 19 whose base overlaps the clip and spreader arms 9 and 11 . the guidehead 19 is intended to facilitate the introduction of the clip 1 &# 39 ; in the locating hole 15 and to prevent premature spreading of the clip arms 9 should they happen to strike one side of the rim of the hole . the same function can also be performed by projections 20 formed on the clip arms 9 and indicated in the fig1 and 3 in the form of chaindotted lines . as an alternative to the break edges at the deliberate frangible point 7 , these forming the detent edges 17 , the deliberate frangible point may be arranged at one of the long sides of the rectangular shank 6 towards the supporting disc 8 while the transverse sides of the shank 6 are remote from the supporting disc 8 so that the detent edges 17 cooperating with the grooves 13 can be shaped right from the start in a desired manner . in amplification , it may be pointed out that the diameter of the sealing collar 5 is made larger than that of the supporting disc 8 in such a fashion that it overlaps the latter and thus seals the locating hole 15 in a known manner . it is to be understood this invention is not limited to the exact constructions illustrated and described above but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the following claims .