Secondhand Mods is a California-based retailer serving watch modders and enthusiasts worldwide. The company buys and sells used watch parts, while its Permanent Collection features new parts designed and manufactured by Secondhand Mods. The site highlights more than 2,500 parts from over 150 suppliers, with new items added daily.

Its extensive catalog covers components for popular Seiko models, including SKX007, SKX013, SRPD, SRP Turtle, SRPE, Monster, and 62MAS watches. Shoppers can find bezels and inserts, cases and casebacks, chapter rings, crowns, crystals, dials, hands, movements, and movement parts, along with tools and spare parts. The store also offers watch bracelets, straps in a range of widths, end links, buckles, and clasps.

The Permanent Collection includes custom case bundles, sapphire crystals, bracelets, crowns, and other components, as well as regulated Seiko NH-series movements. Secondhand Mods also sells genuine Seiko parts, including bezels, dials, cases, bracelets, and movements, alongside selected Tudor parts and complete watches. Customers can explore new arrivals, sell parts to the company, and access shipping information and discounts.