Production networks have been extensively developed in East Asia. Previous studies on production networks used international trade data or input-output tables, but such aggregate data cannot explain how the networks actually operate. With the aim of understanding the features and characteristics of East Asian production networks, this paper examines the procurement system of a HDD assembler operating in Thailand. This micro-level case study found that this particular production network consists mostly of arm's-length suppliers, who are independent and on an equal footing with the assembler. These arm's-length suppliers are mostly located in the assembling country, but some are located in neighboring countries. This proximity is necessary to establish good relationships between customer and suppliers and allows problems to be solved as soon as they occur. The arm's-length suppliers engaged in each country's leading industries, such as the electronics industry in Malaysia and Singapore and the automobile industry in Thailand, have extended their business to supply the HDD industry. These suppliers have formed an industrial cluster in each country within a two- or three-hour drive area. Each cluster that spans different countries is linked by a well-developed logistic network that employs the just-in-time production method that prevails in East Asia. On a regional level, these separate clusters tend to form international production networks that connect to each other across neighboring countries within a distance that provides a quick response time for problem solving. This study also found that American HDD assemblers outsourced indigenous suppliers in Malaysia and Singapore because American suppliers did not follow the assemblers' move to the region. However, since Japanese suppliers did follow the Japanese HDD assemblers to the Philippines and Thailand, indigenous suppliers were not outsourced.