This is actually a Corning Celcor Monolythic Substrate Ceramic (cordierite, mullite) honeycomb block used for the manufacture of an automotive Catalytic Converter.

Blocks like this can be used for jewelry and other delicate & intricate soldering. The block can withstand temperatures of up to 1200c (2192F), and occasional 1400c (2552F). Very resistant to shock for temperature changes.

This asbestos free ceramic round soldering block contains thousands of perforated tiny holes, improving heat dissipation for finer soldering. Tiny holes or perforations in the soldering board can hold earrings posts or other pins. It allows you to pin or hold down tricky shapes and also provides more even heat dissipation. Also binding wire can be used pressed into the holes in the block to pin or hold down pieces while soldering.

Dimensions:          4.662” diameter x 2.874” tall (118.4 mm dia. x 73 mm tall)