Splines and serrations

Splines and serrations are repetitive features comparable to screw threads. Similarly, it is not necessary to give all the details of the splines or serrations, the symbology does it for you. The convention is that one line represents the crests of the serrations or splines and the other the roots. This is shown in the hypothetical drawing in Figure 3.17 where there is a spline at the right-hand end of the gear drive shaft. A note would give details of the spline. The standard ISO 6413" 1988 gives details of the conventions for splines.
Engineering Drawing for Manufacture
by Brian Griffiths
Publisher: Elsevier Science & Technology Books