Tham khảo tài liệu 'sổ tay tiêu chuẩn thiết kế máy p25', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | __CHAPTER 21_ THREADED FASTENERS Joseph E. Shigley Professor Emeritus The University of Michigan Ann Arbor Michigan SCREW THREADS BOLTS SCREWS NUTS TAPPING SCREWS REFERENCE This chapter is intended to cover the description uses materials and sizes of threaded fasteners. The amount of data available concerning this subject is extremely large so the intent here is to provide the information necessary for the usual machine-design task of selecting such fasteners. The data contained in this chapter have been compiled in part from the standards listed in Ref. . SCREW THREADS Standard screw threads consist of the Unified inch series and the metric series. Two profiles have been standardized in the metric series these are called the M and MJ profiles. Figure shows that both the Unified and metric M threads utilize the same profile. The metric MJ profile has a rounded fillet at the root of the external thread and a larger minor diameter of both the internal and external threads. This profile is used for applications requiring a high fatigue strength and is also employed in aerospace applications. The Unified-series profile shown in Fig. is designated as UN. Another unified profile designated as UNR has a rounded root on the external thread. Unified thread standards are based on the nominal size major diameter and the number of threads per inch. The three standards coarse UNC fine UNF and extra fine UNEF are listed in Table and are called the standard series. Typical specifications would be written J4 20 UNC or -20 UNRC Both these designations specify a nominal size of in and 20 threads per inch. A constant-pitch unified series consisting of 4 6 8 12 16 20 28 and 32 threads per inch has also been standardized. These are used mostly for sizes over 1 in and 8 UN 12 UN and 16 UN are the preferred pitches. STANDARD HANDBOOK OF MACHINE DESIGN FIGURE Basic thread profile for .
