28 of the lower arm 16 will engage the front surface 9 of the support bar 3 at a point above the rounded corner 5 such engagement is provided to prevent the face 49 from contacting the rounded corner 5 and thus assists in preventing rotation of the retainer clip 12a in a counter clockwise direction shown in fig3 in similar manner a second retainer clip 12b may be positioned adjacent to the right support arm 2 and a third retainer clip 12c may be positioned at a point on the support bar 3 intermediate the first retainer clip 12a and a second retainer clip 12b following installation of the retainer clips 12 the retainer bar 56 is positioned in front of the printed wiring boards 11 with the back portion 58 in alignment with the retainer slot 40 of the extension 33 and the back portion slid into the retainer slot 40 in each of the clips 12 in such position movement of the printed wiring boards 11 out of their card slots 6 will be resisted by the toe edge 61 of the foot portion 59 acting against the front edge 64 of the printed wiring board 11 in the event that it becomes necessary to remove a printed wiring board the retainer bar 56 may be vertically lifted from engagement of its back portion 58 with the retainer slot 40 thereby freeing the printed wiring boards 11 for removal a storage slot 50 has been provided in the lower arm extension 34 of the lower clip arm 16 to ensure that the retainer.