The spring can be considered as the trace, or locus, of a moving point — therefore it has a starting point — and that's the first thing Catia asks for. So, it is at the radius distance away from the centreline, and it's going to wind along and around the line. The Pitch should be self-explanatory, but the Height would've been better off being called Length — because it's asking, 'how long is the spring?'
At the Helix default setting, the 'Revolutions' box is in-active, this comes to life when more complicated options are used. In this case it's not required as the pitch and so-called height (length), effectively define it.
Once it's clear what's happening, then try using the other parameters. There's so much that can be done with this Helix command — and when all the options have been used, even more complex helices can be made by using swept surfaces — controlled by the powerful Law tool. Click
here to see some examples.
To finish off the extension spring a simple Swept Surface has been run along the helix...
The hook ends shown, are just constructed by eye for pictorial purposes — there are so many types of spring end - and most of them are of simple geometry.
