I believe it is the Volume Selector. It makes it so that it selects vertices or faces that are contained within a specific volume(box,sphere,cylinder, etc).
http://deicidenbf.thanez.net/ and http://www.winzipification.com/References/ have lots of references. Plus you can always check manufacturer websites, enthusiast forums etc.
There is so much to consider about the proper glass and fluid material etc.. you may have a look at this other forum BenderArtists.org: accurate-liquid-in-glass-rendering ?? ( sorry i didn't follow any thread here about this topic :wink:)
using floaters will probably be the fastest method for making those screws if you plan to bake it down. A word of warning though if you do plan to bake this into a LP using floaters. The "thicker" the screw, the more you have to push your cage, making it less accurate and prone to making warped normals on the edges around…