The telescopic Plunger arm has four main components: ball; outer tube; inner rod; plunger / sucker / manipulator cup. The outer tube and inner rod form a telescopic sliding assembly.
The as mentioned in the Eye Stalk page I bought some hardwood balls from eBay of the right diameter.
I drilled a hole though, and a counterbore into the ball. The hole was the right diameter to allow the inner rod to pass through, while the couterbore was the right size to give the outer tube a socket to locate in.
Using some left-over plumbing ABS plastic pipe which just happened to the right diameter, I made an insert for one end to close it down to the right diameter for the inner rod to pass through. It was made using an offcut of the plastic, slotted, made smaller with a hot air gun, and pushed in. Fixed into place with some solvent, and made good with a touch of car body filler.
The inner rod was made form a piece of wooden dowel that used to be a cupboard clothes rail, and again just happened to be the right size!
The rod was painted, snaded, painted, sanded unitl I got a good finish, then was given a silver paint finish (old alloy wheel tough-up paint)
Not made yet, but I have ideas on vacuum forming a plastic plunger of the right size, unless I can find a black small sink plunger in the meantime
I used the inner rod as a guide to make sure I glued the outer tube into the ball's couterbore, concentric to the hole previously drilled for the inner rod.
So with the inner rod in place, and outer tube slid over it, I carefullt applied some areldite to the end of the tube and eased it into the couterbore, making sure not to get any on the inner rod, as I didn't want that glueing in place!