Celestron F6.3 reducer corrector.
There is a small chip on the top element. I've marked it on the last pic with a red circle
Comes with SCT to 2 inch adapter and SCT to M42 adaptor.
Which means it can be used with a refractor! 
Selling because I already have a 0.60 altair astro reducer which works really well with my 80ED.
BTW I also have a SCT diagonal for sale on here.
120 posted in Aus with the adapters
OR
90 posted without adapters