Rotating Rings that allow the rotation of a Newtonian OTA around the optical axis for easy repositioning of the eyepiece. These rings can accommodate an OTA up to around 365mm (14 1/3") in diameter and are very well made / heavy duty. The slightly larger 15" rings are currently going for $900 US, wowzers..
http://www.parallaxinstruments.com/r...tml#ringprice2 The size was custom made for my 12” Newtonian but in the end the OTA was slightly smaller so I had felt lined spacers that I will throw in if you like. Yours for
$400 plus postage.