It's 4mm i think , it was just a mock up , i honestly expected it to cause more problems than it solved so i needed to keep the option of returning to standard , but i'm very happy with the results and tommorow the place i buy my steel from will be open so i will have more choices then .
Now i have a working template i might make it a bolt on part .
Incidentally having done this i reckon the Man a Fre caster brackets would be fine for a manual truck , they just need trimming with a grinder .