GC ELECTRONICS' 21-166 is a positive pre-sensitized phenolic circuit board ideal for hobbyists and professionals alike. This board features a 1/16" thick phenolic base with one ounce (0.0014") copper, coated with a positive photo etch resist. It's designed to be used with GC Developer (Part Nos. 22-225 or 22-226) for precise etching. The peel-off coating protects the board during handling and cutting, ensuring a clean and professional finish. This board meets Fed. Spec.: S-10941-1.