The Movcam 130:80mm Step-Down Ring allows you to mount 80mm lenses onto 130mm clamp-on matteboxes - the kinds without a thread on their rear adapter.

The ring is split along a point of its diameter to flexibly widen and mount a mattebox. (A locking pin on the side of the mattebox securely tightens the ring in place)

Used but in great condition. Buy it now for $59 or send an offer. Shipping is worldwide