The Explore Scientific Hexafoc 2.5" Adapter for 3" Corrector is a ring which mates Hexafoc or Hexfocus-enabled telescopes - particularly the Explore Scientific range of Triplet Apo refracting telescopes, with the Explore Scientific 3" 0.7x Reducer/corrector.
This ring fits to the rear thread of the Hexfocus drawtube, once the 2" eyepiece holder with compression ring is removed and then provides a male thread for the Explore Scientific 3" 0.7x Reducer/corrector's 3" nosepiece internal to thread on to.