Rack makers sell these; for example https://www.budind.com/racks-cabinets-accessories/ or https://www.dell.com/en-us/search/server%20rack%20shelves but I would expect any number of places that produce racks have them. I have an H960 and needed a solution for a 3U 19 storage array that can attach in the front but needs more support and doesn't mate up with the H960 rear rails. So rather than spend significant money on a shelf, I just installed a pair of angle irons from front to back (vertical flange down) and set the array on that. Since it's close to 19 inches wide, that simple solution fully supports it. For a heavy oscilloscope I wanted to install as well, I did something similar: angle iron supporting a sheet of plywood. In that case, it has some additional angle irons running across, to keep the plywood from bowing under the load. paul

I'm unable to find original Chassis-Trak rails where I am so I fit DEC gear into H960s using modern server rack rails, cheap cabinet rails and aluminium angle, and they all work acceptably. Modern servers aren't anywhere near old DEC gear in weight so the thin modern rails are out but there are rails (about 80 to 100mm wide, lying flat) where a pair are just thin enough to support say a BA11-K sliding through the front of the H960. They are always adorned with all manner of quick-release levers and pivoting brackets so some angle grinder, Dremel and pin punch work soon removes all this. Then they need to be cut down, sometimes this can be done without fully disassembling and losing ball bearings by using a Dremel and a few reinforced cut-off wheels. Once trimmed I drill the far ends and put a small screw through to prevent the inder rails sailing out the back. Cabinet slides are dirt cheap and plentiful and I recently used some for Diablo racking. I decided to put them on 3mm aluminium plates with heavy al angle (all from scrap) along the sides. There are locating/locking pins at the back that function like the original Diablo slides. https://forum.vcfed.org/index.php?threads/what-do-your-happy-places-look-li… For plain shelving, I've found 3mm x 3mm x 25mm ( 1/8 x 1/8" x 1") al angle works fine is the least effort. I made a simple 3D printed drilling jig for using this in an H960 so the top of the inside surface is at the lower edge of the DEC gear. Two are needed. Press fit the jig into the H960 side holes, clamp the al angle onto the jig and drill 15/64" through, then self-thread 1/4-20 screws and it's done. https://www.thingiverse.com/thing:4311796 The one thing that's consistent in all the above measuring marking scribing cutting bending drilling threading is that nothing is consistent. Steve.