an i o shield opening in accordance with an nlx form factor specification as discussed in the background of the invention the described way of forming the opening 133 is advantageous in that it requires fewer manufacturing steps than current chassis accordingly fitting the slot bracket 123 in the opening 501 to form the opening 133 is a convenient way of providing slots for i o expansion ports and a i o shield opening in accordance with an nlx standard additionally the configuration helps to minimize the profile of elevation of the chassis furthermore the configuration of the slot bracket 123 assists in providing rigidity to the back wall 113 the chassis 100 may comprise three slots 147 in the slot bracket 123 three corresponding cover pieces 125 and a retaining bracket 127 capable of being mounted on the slot bracket 123 to hold at least one of the cover pieces 125 in place for example the retaining bracket 127 may comprise a back portion 151 a side portion 153 and a top portion 155 the back portion 151 may be substantially flat and have a plurality of openings 157 which are capable of receiving catches 159 extending from the back wall 113 and extending upward the retaining bracket 127 may be mounted on the back wall 113 by inserting the catches 159 in the openings 157 and advancing the retaining bracket 127 downward to a locked position the side portion 153 extends perpendicularly from the back portion 151 adjacent the.