Mark’s clamping molds conform to the irregular shape on the inside of the guitar and result in him being able to apply much more even clamping pressure when he glues on the bridge and fretboard extension. Both the bridge and the fretboard extension have large surface areas. With these molded cauls on the underside he can apply a lot of clamping pressure without damaging anything. Here’s a photo of the two molds. You can see the impressions of the bridge plate, popsicle brace, X braces, and upper transverse brace. The molding compound is a thick layer of a pasty consistency plaster (Fix-it-all) and backing blocks are 1” plywood.