The Track to Track (TT) distance is specified in mm and is one of the parameters that determines the pattern class of the board.
A typical TT value is 0.150mm or 6mil. This is the value for our pattern class 6 our standard.
We define OTT as Outer layer Track to Track distance and ITT as Inner layer Track to Track distance.
Insulation is defined as
The insulation distance may not be reduced to less than 75% of the nominal distance (including unwanted random particles).
R1 > 0.75 A1
R2 + R3 > 0.75 A2