The American Society of Mechanical Engineers provides a set of common standards used by industry for placement of dimensions.

When extension lines or centerlines cross visible object lines, gaps should not be left in the lines.

In a group of parallel dimension lines, the dimension values should be staggered.

It is more difficult to manufacture a part designed using two decimal places than the same part using four decimal places.

It is permissible to letter a dimension value over any line on the drawing.