You can maintain the parametric relationships between labeled dimensions by locking them. To lock a dimension directly in the drawing area, click 
next to the dimension.
When a labeled dimension is locked, all of the associated parameters also lock. This means that as the dimensions are moved in the drawing area, the associated parameters are constrained and the dimension value is preserved.
Note: Locked dimensions and their associated parameters cannot be changed in the drawing area. Use the Lock column in the Family Types dialog to change them.
When a labeled dimension is unlocked, all of the referenced geometry unlocks and is unconstrained.
To lock a labeled dimension from the Family Types dialog
- Click a dimension in the drawing area.
- Click Modify | Dimensions tab
Properties panel
Family Types. - Select Lock to constrain a parameter.