I have successfully installed the screw plugin, thanks anyway Chris. I'm trying to install the FredoScale plugin but my problem is I can't find it on plugins menu even I downloaded the latest version together with ZLoader_FredoScale.rb I can't find also the the submenu "Fredo6 Collection" on Sketchup tools to make use of these icons. Can you help me with this one Chris? Thanks again.

There are several good plugins to help with making helical forms BUT you can do it 'by hand' quite easily - e.g. see here for some ideas http://forums.sketchucation.com/viewtopic.php?f=15&t=9097&p=55538&hilit=helical+ramp#p55538 ...