Non-Stick Clamping Cauls for Resin Casting (set of 6)
These are various-sized blocks of HDPE or UHMW to use as hold-down clamps.  Place them on top of objects you want to clamp or weight down to prevent floating in the mold.  The blocks protect your clamps from the resin, and they do not harm the surface below.    They can be stacked, if needed, to apply pressure where the clamp can't reach. 
The package contains a variety of sizes, including one long, one larger, and 4 smaller random size blocks.  The edges are softened for easy handling.