See the photo report: a new Mars Discovery coil for Garrett AT PRO. Round, 13 inches, DD coil type, designed for universal search.
Recovery speed test
Here’s the MarsMD 13 Discovery coil from MarsMD, the alternative manufacturer. Coil type: DD. Coil shape: round. Size: 13 inches (33cm). Produced for different metal detectors. For the Minelab X-Terra series, this coil also comes in two frequencies.