{"id":5726,"date":"2026-09-18T10:00:17","date_gmt":"2026-09-18T01:00:17","guid":{"rendered":"https:\/\/ohtavn.com\/?post_type=media&p=5726"},"modified":"2026-09-09T13:18:49","modified_gmt":"2026-09-09T04:18:49","slug":"complete-comparison-of-metric-and-inch-threads","status":"publish","type":"media","link":"https:\/\/ohtavn.com\/en\/media\/complete-comparison-of-metric-and-inch-threads\/","title":{"rendered":"A Complete Comparison of Metric and Inch Threads: A Practical Sourcing and Design Guide for Manufacturing Industries"},"content":{"rendered":"
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Introduction<\/h3>\n<\/div>\n
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In manufacturing, “screws” are the most fundamental and critical components supporting product reliability. However, in design and procurement, confusion between “metric screws” (the global standard) and “inch screws” (still widely used in aerospace, hydraulic equipment, and products for the U.S. market) can lead to serious trouble. Particularly in Vietnam, which is attracting attention as an overseas production base, the mixture of Japanese, Western, and local standards makes it essential to use the correct type based on accurate knowledge.<\/p>\n

In this article, we provide a thorough explanation ranging from the structural differences between metric and inch screws to international standards (ISO, UN, etc.), as well as the “Zero-Mistake” procurement and quality management techniques advocated by Ohta Vietnam. By reading this article, you will acquire specific methods to prevent fastener selection errors and balance cost optimization with quality improvement.<\/p>\n<\/div>\n

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Metric vs. Inch Screws: Critical Differences in Basic Structure and Standards<\/h3>\n<\/div>\n
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Definition and Characteristics of Metric Screws (M-threads)<\/h4>\n<\/div>\n
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Metric screws are the world’s most widely used screw standard, defined by the ISO (International Organization for Standardization). Nominal diameter (outer diameter) and pitch (the distance between threads) are expressed in millimeters (mm). For example, “M8 x 1.25” indicates an outer diameter of 8mm and a pitch of 1.25mm. The thread angle is fixed at 60\u00b0, making calculations easy and versatility high. Japan’s manufacturing standards also comply with these metric threads, offering the advantage of easier component standardization and cost reduction.<\/p>\n<\/div>\n

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The Complex System of Inch Screws (Unified and Whitworth Threads)<\/h4>\n<\/div>\n
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On the other hand, inch screws are based on the unit of 1 inch (25.4mm). The current mainstream is the “Unified Thread,” standardized across the United States, Canada, and the United Kingdom. Unified threads include UNC (Unified Coarse) and UNF (Unified Fine). While the thread angle is 60\u00b0 (same as metric screws), the size notation follows a format like “1\/4-20” (meaning a 1\/4-inch outer diameter with 20 threads per inch). Furthermore, in older equipment or construction materials, “Whitworth threads” with a 55\u00b0 thread angle may still exist. Confusing these not only makes physical fastening impossible but also poses a risk of damaging components by forced tightening.<\/p>\n<\/div>\n

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Why Standard Selection Affects Product Lifespan and Cost<\/h3>\n<\/div>\n
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While many Japanese companies use metric screws as their standard, the adoption of inch screws becomes necessary for products exported to North America, construction machinery, aircraft-related parts, or maintenance of old British-style equipment. The key here is not just matching the size, but also understanding the standards for “strength classes” and “surface treatments.” For instance, while metric screw strength classes are labeled as “8.8” or “12.9,” Unified threads use unique notations such as “Grade 5” or “Grade 8.” Misinterpreting these compatibilities can lead to unexpected breakage accidents.<\/p>\n<\/div>\n

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**Key Data: Statistics on Global Screw\/Fastener Market and Standard Usage**<\/div>\n<\/div>\n
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