You will be bidding on a Brunson Model 88 Tilt Mounting Base.

A heavy steel plate provides support for two bronze vees spaced on 9 1/2" centers. The vees provide stable support of the instrument barrel. The 88 base has a tilting range of approximately 1 1/4 degrees both horizontally and vertically. Tilt is controlled by large headed, fine thread screws for easy adjustment. The carrier may be rotated with respect to the bottom plate through 360 degrees and clamped in positiion by socket head set screws