The numerous stylistic devices in Technical Illustration allow you to visualize technical coherences. An important, but very often underestimated, method in Technical Illustration is the omission of lines, which often helps to display the desired information more clearly.

This sounds contradictory, but is actually a vital factor in the creation of technical illustrations.

When an illustration contains too much information, it looks like a tangle of tiny details when printed, for example. On the other hand, the technical illustrator must invest the appropriate effort to display all vital elements of the illustration. 

What the spectator notices first in an illustration where "omission" was applied; interceptions (so-called "inner lines") in lines and ellipses. Simply put, these are spots where the light is reflected and which cannot really be seen up close.

Here is an example:

You see two representations of the same part: the left one with intercepted lines and the right one with all lines drawn through. The interceptions in the lines lets the illustration look more vivid, while the variant with the drawn-through lines looks rather rigid.

Before intercepting lines in your illustration, imagine a light source that reflects off the depicted part. By doing this, you can quickly locate those spots where an interception makes sense.

How you use this stylistic device is in the end a matter of your personal taste and your "handwriting" as technical illustrator. If you distend its application, however, your illustration can "break apart". Just try out some possibilities and experiment with this technique.