Image segentation - isolating a grey ish feature

Hi there, I am having some trouble segmenting an image (see attached file, low resolution - original exceeded 5MB limit for this forum).

My goal is to isolate the beam. I have been attempting this by creating a mask around the beam in the image, removing the other features (ie red background, test apparatus and paper ruler).

I have had some luck in removing the red background and test apparatus but find it difficult to remove the paper ruler as the RGB values are very similar to the RGB values of the beam.

If you have any advice on possible methods of separating the paper ruler from the beam, it would be great.

For clarity the red back ground is made up of the red cardboard and some pieces of tape holding it in position. The test apparatus is the silver and black machine on the left hand side. The beam is the slender feature of interest attached to the test apparatus. The paper ruler is glued on top of the beam.