Movcam 144:100mm Step-Down Ring for Clamp-On MatteBoxes

The Movcam 144:100mm Step-Down Ring allows you to mount 100mm lenses onto 144mm 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)