The first table I saw with a reflex clamp was the Oracle Delphi. As described above, a thin (1/16") washer is slid down the spindle and onto the platter---under the LP, which of course raises the LP off the surface of the platter by the same height. The reflex clamp is then tightened down onto the LP, slightly bending it and securing it to the platter, in the process removing all but the worst warps.
VPI’s first table---the HW-19, was of the same design. Both the Oracle and VPI clamps were threaded (as were the top of the platter spindles), and the underside of the clamps dished (raised around the perimeter on the underside).
BDR made a reflex clamp with the same threading as VPI: 1/4-20, both as a 1-piece and a 2-piece. Both also had a dished underside. @slaw decided using a clamp provides a pathway for bearing noise to make it into the PVC of the LP. so sold his BDR clamp. I still have my 1-piece.
Herbies makes a washer specifically for use with reflex clamps, made of their proprietary damping material. 1/16" thick, 1-1/4" diameter.
