Lettering is a dying art that presents text, dimensions and notes that are hand written in a standard form. Lettering is typically all upper case without slant or formatting but the creator of a drawing will often put their own personality into the lettering. All caps on an engineering drawing is not "yelling" but is good practice and facilitates clear communication. Slanted lettering may be used for emphasis of a particular point or idea.
Letters are all block letters generally of equal width and 1/8 inch tall. The use of a mechanical guide or construction lines to control height is recommended for consistency. Unless an inked drawing is lettered using a Leroy scriber (now obsolete) lettering is done freehand. All letters are upper case only unless in a long paragraph of more than 2 sentences. Letters of a word will be close to each other without touching. Space between words is about the same as the letter H or W. Numbers are the same size as letters. Fraction numbers are slightly smaller than 1/8 inch, stacked and symmetrical to the line it is in. Multiple lines of text should leave space between each line of about half the height of a normal letter.
Special cases of lettering may be smaller or larger than the standard height. Title block lettering may be larger. Section view identifiers and cutting plane labels may also be larger.
Each letter is generally created from top to bottom and left to right. At the end of each straight leg or line of a letter, the pen or pencil is picked up and relocated for the next line. For example the letter 'A' consists of a stroke down and to the left, down and to the right and a final stroke left to right half way up the height connecting the two legs together. Rounded letters such as 'O' start at the top and go down and around to the left to the bottom, pencil up, then another stroke from the top then down and to the right closing the O at the bottom. Shortcuts are often taken making these letters with one stroke. Letters are generally sans-serif though using she serif form of 'I' as the word I is accepted.
Notes on special letters and numbers:
The letter 'W' has both outside legs slanted outward and are not vertical.
The letter 'M' outside legs are vertical and not slanted. 'M' is not an upside down 'W' and vice versa.
The number '0' (zero) and '7' do not have a slash.
The number '4' comes to a point and is not open.
The number '8' is made of two small circles of two to four strokes and not a single figure eight stroke.
The number '9' is similar to the number '6' being made of curved strokes and no straight lines.