When fitting solid rack mounts you
MUST either refit those plates or something else to stop the rack shifting from side to side as you turn the steering wheel.
I've pretty much kept this to myself due to the embarrassment factor, but when I fitted aluminium rack mounts about a year ago I left those plates out (not sure why).
Everything was fine - I took it for a blast along the narrow winding roads along the North Norfolk coast with my better half in the passenger seat - and we stopped for chips at Wells Next The Sea. Lovely.
When we set off for home, however, I pulled away from the roadside and turned the wheel, but the car kept going straight on. I stopped and then found that I could turn the steering about half a turn either way with no movement on the front wheels at all.
Taking a look underneath with wifey twirling the wheel I could immediately see what the problem was. The engine had leaked a bit of oil onto the rack mounts, lubricating them nicely, and breaking the friction that'd been the only thing holding the rack in place within the mounts. As I had no tools I had to call the RAC, and the man with a van came up with a simple solution and fitted a jubilee clip to each end of the rack outboard of the mounts, effectively filling the gap and keeping the rack where it ought to be.
The consequences of the rack working loose to the extent it did if we'd still been thrashing along those winding back roads doesn't bear thinking about.
That was supposed to be a temporary fix, but it's still there now and passed its last mot with them in place, so it can't be that bad, but I really ought to put those plates back in. If only that didn't need the engine lifting off its mounts...