Blue Sea Fuse Block Ato 12 Circuit W/Gr Thermoplastic Base & Polycarbonate Cover FUSE BLOCK ATO 12 CIRCUIT W/GR. Clear insulating cover with label recess for small Blue Sea Systems' labels. Cover insulates all conductive parts, satisfying ABYC/USCG requirements. Tin-plated copper buses and fuse clips give 30 Ampere rating per circuit. Thermoplastic base and polycarbonate cover.