Interpart Expression: To create or edit a link to an expression in another part.
To apply tolerance and link two dimensions in assembly.
Step 1: Create The New Expressions.
First open an assembly to create interpart expression.
You can see my tutorial to create an assembly.
Now create expression in the assembly.(Menu>Tolls>Expression).
Create two expressions as shown in Picture.
Now apply these expressions to the components of assembly.
Make cylinder as a work part.(Double click on the cylinder in assembly navigator.)
select the dimension of the hole that you created in cylinder for the piston rod.
See this picture go through Diameter>option>Formula.
You can see this dialog box.
In the formula you have to define the relation in form of interpart expression.
Click on Create/Edit Interpart Expression.
Call the expression named "Dia".
Then press "+".
Call the expression named "Tolerance".
You can see this formula.
The interpart expression for cylinder hole is created.
Step 2: Define the Interpart Expression.
Now make Piston as a work part to define the diameter of piston rod.
Select the dimension that showing the diameter of piston rod.
Go through Interpart Expression.
Select the expression named "Dia".
So the Diameter of hole in cylinder and the diameter of piston rod both are linked.
If you can change the value of Expression, The change will occur in both the components of assembly.
you can check the interpart expression by just changing the value of the expressions.