Wasserhahn (Water Tap) by Roger D

Here's a description of the puzzle from puzzlemaster.ca:

Wasserhahn or "Water Tap" in English, is a puzzle by the infamous "Roger D".  Roger D is a mysterious puzzle designer from Germany, and his actual identity is known only to a few. Roger is known throughout the puzzling world for his extremely difficult and high quality machined aluminum puzzles. Roger's puzzles are produced in relatively small numbers and are highly collectible, they are also sold with no information as to the objective of the puzzles and this is classed as adding an extra degree of difficulty to them.

This puzzle is made of aluminum with a copper spout at its front and two butterfly nuts at its top.  The front of the puzzle bears the initials of the designer.  To solve this puzzle you must figure out how to make the tap start working...  A difficult and creative solution to an amazing and collectible puzzle gem.