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I'm trying to use the 'thread making screw' to ground my Dell PDU to the Rack, however the metal on the rack is impossibly hard. Is this even required? The included screws don't even seem "thread making" or "self tapping".

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Never heard of that "thread making screw" procedure (which isn't to say it doesn't exist, but I've never seen it).
Most racks will have an earthing lug on them - Just bolt the PDU's rack ground line to that & you're all set (as a bonus that lug is usually bonded to all the metal bits of the rack so you're guaranteed to be grounding everything that should be grounded).

As to whether the grounding is necessary, it's certainly a good idea (If something goes catastrophically wrong and mains power somehow gets shorted to the rack rails this gives it a better path to ground than "via the datacenter technician's body"). Necessary may vary according to local codes, but I would definitely recommend it.

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It also reduces the chance of the rack becoming a "floating" voltage potential different than the AC mains ground potential, which is the reason you'll see metal cable trays sometime have them. The other reason why bothering is good (besides trying to meet building / safety code, e.g. NEC in US and Canada, is to prevent insurance or warranty claims being revoked) is to reduce risk of static electricity zapping the many static sensitive components in computer systems. – mctylr Apr 13 '10 at 18:57
@mctylr good point about the ground-potential difference (especially if the site has a dirty ground). – voretaq7♦ Apr 13 '10 at 19:01
thanks for that. Here's the PDF manual. See "Connecting the ground wire" > support.dell.com/support/edocs/systems/smarcon/en/pduii.pdf I ended up brute forcing the screw into the rack hole. It was a ridiculously tight fit and required me to leverage the screw driver with an adjustable wrench. – Mindflux Apr 13 '10 at 19:22
@mindflux Looks like they just assume you don't have a dedicated ground lug -- you're already connected so I wouldn't go crazy about it, but if you can find grounding lugs in your racks they're bound to be less trouble than brute forcing the screw :) – voretaq7♦ Apr 13 '10 at 19:51
I thought I could use a lug on the rack but I didn't take the time to find one so I was just 'following directions'. It's a Dell Rack, so maybe this is the only way to do it (as shown above). I'll have to look more closely for any lugs I might be able to utilize. – Mindflux Apr 14 '10 at 3:52
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