Defined variables in Custom properties to vary the dimensions in a sketch

Hello.

I have a problem that I haven't resolved yet.

In my custom properties settings I have a Property name [Coating] that is defined by a drop down list with two values that is [B1] and [B2]

I want to define a dimension in a sketch with this two values.

B1=1mm

B2=2mm

How do I set the connection between the values B1 and B2 to be 1mm and 2mm?

I have tried with the equations manager an d global variables, but with no success.

Any suggestions?

SolidworksParts And Features