fig3 slot 23 of the same structure as slot 20 extends along the inner surface of the opposite edge wall 15 preferably the slots 20 and 23 extend from the entrance opening 2 to at least the midway point between the entrance opening 2 and the end wall 14 so that the outer edges of the disk are engaged from the point of entry of the edges to the enclosure to the point of engagement with the grip elements 17 and 18 on the end wall 14 similarly upon removal of the disk from the enclosure the edges of the disk are engaged to the point of removal of the edges of the disk from the enclosure in the embodiment shown the slots 20 and 23 also extend to the entrance region 2 in order to provide a securing engagement for the cover for the enclosure 10 as will later be explained the entrance regions of the slots 20 and 23 may be tapered in the vicinity of the opening 2 to facilitate entrance of the disk into the slots the outer edges of the edge walls 15 and 16 are preferably serrated as shown in fig1 and in the enlarged view of fig4 to facilitate gripping the enclosure 10 for insertion.