I took my engineer cover off on my old Vauxhall so I could remove and clean the plugs when I was having starting issues but didn't put it back on straight away. Yes you've guessed I put them somewhere safe so I wouldn't lose them, so safe that I need to buy a couple more. They only hold a plastic cover onto the top of the engine, for aesthetics' id imagine, and im really not paying £6 for to silly bolts so I just want to buy something non specific but I don't want to put steel in if that's going to cause an issue, they are M6x18 torx but I'm quite happy with allen or a normal bolt. This is the offending part complete with 1 year warranty lol.
As long as you have the right thread, material doesn't matter if they're not load-bearing. Put some anti-seize (copper slip, never-seez, super-high-spec-Molybdenun-Disulphide-based stuff, it'll all work the same) on them and you won't have issues when it comes to removing them again - good practice for any fastener that doesn't need to be threadlocked, dissimilar metals or not.
