Unfortunately they come with the chassis and are not offered by Dell for sale that I can find. I did find a compatible set here - www.racksolutions.com/shoulder-screws-nuts.html Let me know if this helps.
Hi I'm not sure what they are called but my PE2950 is missing the side 'mushrooms' for rack mounting. These are the parts that fit onto the threaded studs in the side of the chassis (3 each side) that then drop into the sliding rails. The bits circled in red: [IMAGE] Is it possible to buy these from Dell? I've not managed to find anything so far. Thanks,  Simon
PE2950 missing side 'mushrooms' for rails