Retail ($1695.00).
I bought mine from a local hobby shop…this is the only 1/8" (black) shaft collars I see on eBay, but there nice in (black) also;
http://www.ebay.com/itm/1-8-Bore-Shaft-Collar-With-6-32-Set-Screw-Black-Oxide-Finish-SC125BO-/260976963313?pt=LH_DefaultDomain_0&hash=item3cc3706ef1
I did something similar to my first pair of 80's with knurled thumb screws going through the back side of the rod blocks, but didn't last…they kept backing out and eventually the plastic thread (rod block) stripped, so I would have had to press a threaded metal/aluminum sleeve into the rod block for it to work properly, but then found the shaft collars in my box of stuff from a remote controlled car I had built in 1991, so I used them instead. The shaft collars are actually better because they allow the cups to swivel freely to the shape of your head/ears.
Thank you, I use them on all of my Grado's to keep my desired height.