Seiko SPB321
The Seiko Prospex SPB321 is a modern reinterpretation of the classic 'Sumo' dive watch. It features a 45mm stainless steel case with super-hard coating, a blue dial, and a blue ceramic unidirectional bezel. Powered by the Seiko 6R35 automatic movement, it offers a 70-hour power reserve.
Specifications
Movement
More from Prospex Sumo
View all Prospex Sumo references →Related Guides & Articles
The best watches you can buy under $1,000 in 2026 — pre-owned and new picks from Seiko, Hamilton, Orient, Tissot, and G-Shock with current prices.
Current secondhand Seiko prices — from the Seiko 5 to Presage and Prospex. See pre-owned median prices, ranges, and the best Seiko watches to buy used.
Learn how to compare pre-owned watch prices across marketplaces — understand market value, spot overpriced listings, and find the best deal on the watch you want.
The best deals on pre-owned watches this month — undervalued models from Rolex, Omega, Tudor, Seiko, and more, with current market prices and why they're worth buying.