A mechanism description analyzes (that is, subdivides into components for further scrutiny) an object in space. When you try to organize your major subsections, if no other obvious pattern seems appropriate, you can always fall back on the more-important-to-less-important strategy.

• Don’t sell the object.
  A technical writer is not required to persuade the reader that the object is wonderful, or valuable, or scary. But do mention the details. While you shouldn’t say an object is “adorably cute,” you could mention that it “resembles a cartoon cow wearing a pink ruffled skirt,” and let your readers make the value judgment for themselves.
• Just describe it.
  Provide whatever level of detail your reader requires. Know your audience.  A child safety organization may require an extremely detailed description of a simple toy (along with a separate process description for the manufacture of each component), while a military recruitment office might require only a few paragraphs about a complex nuclear submarine. —Mechanism Description: Writing about the Function, Appearance, and Operation of an Object