Hmm. Snot easy though is it? I even read the workshop section to check, and I'm not sure I understand what you're getting at with the 'keystone' bit.

Maybe it's just the bad light in the workshop, cuz my eyes are perfect.

Or more likely the skinfull I had last night has blurred my brain!
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball