this manner the spool is retained within the cassette fig1 shows a portion a of fig1 in which the formation of the recesses on the side wall of the base can be seen more clearly the spacing between the horizontal recesses 54 and 55 corresponds exactly to the spacing between the spool flanges the lower horizontal recess 55 is arranged somewhat above the bottom wall 51 as the lower spool flange generally does not lie directly on the bottom wall it is obvious that the previously mentioned special features can also be utilized in the embodiment shown in fig1 to 12 for example the horizontal recesses 54 and 55 can be slightly chamfered to facilitate the introduction of warped flanges also the provision of further stopping means is conceivable as shown for example in the central area of the bottom wall as shown in fig1 the following fig1 to 17 are concerned with a further embodiment of the invention in which the projections of the side wall of the cassette base are formed as insertable elements fig1 shows a perspective view of the base 1 of a cassette having a side wall 2 and a bottom wall 3 around the inner side of the side wall 2 of the casette base vertical recesses 14 are spaced these recesses.