1. General Rules of Dimensioning
Place dimensions between views whenever possible
Dimension the most descriptive part or view of the item
Extension lines may cross object lines, but do not break them
Dimension inside a recess if it improves communication

2. Dimension to visible lines only, not to hidden lines
Extension lines may cross each other if necessary, but dimension lines should not cross
Keep dimensions off the objects
Dimension true length lines and surfaces only
Do not use a dimension line for an extension line
Place running dimensions in direct line with each other when possible