Arm 1 moves the metal every third tape loop, therefore the mechanism consisting of arms 1-3 can only produce 3 out of the necessary 4 Quicksilver.
It feels expensive to spend 4i on arm 5 doing nothing but attaching the 4th Quicksilver.
But I stumbled upon this arrangement of arms 4 and 6 for a very elegant assembly using only 6i. In all my other attempts, it was much more complicated to get the thirds of the output to align.