Metric Screw Threads M Profile Machinery's Handbook, 31st Edition
2019
G Tolerance Position for Small Allowance (Fundamental Deviation)
H Tolerance Position for No Allowance (Fundamental Deviation)
Internal Thread
T
+
ES
ES
T
EI
Zero Line
Basic
es
es
T
ei
External Thread
ei
–
ei
T
T
e or f Tolerance Position for Large Allowance (Fundamental Deviation)
g Tolerance Position for Small Allowance (Fundamental Deviation)
h Tolerance Position for No Allowance (Fundamental Deviation)
Fig. 5. Metric Tolerance System for Screw Threads Tolerance Grade: This is indicated by a number. The system provides for a series of tolerance grades for each of the four screw thread parameters: minor diameter, internal thread, D 1 ; major diameter, external thread, d ; pitch diameter, internal thread, D 2 ; and pitch diameter, external thread, d 2 . The tolerance grades for this Standard ANSI/ASME B1.13M were selected from those given in ISO 965/1. Dimension Tolerance Grades Table D 1 4, 5, 6, 7, 8 Table 8 d 4, 6, 8 Table 9 D 2 4, 5, 6, 7, 8 Table 10 d 2 3, 4, 5, 6, 7, 8, 9 Table 11 Note: The underlined tolerance grades are used with normal length of thread engagement. Tolerance Position: This position is the allowance (fundamental deviation) and is indi cated by a letter. A capital letter is used for internal threads and a lower case letter for external threads. The system provides a series of tolerance positions for internal and ex - ternal threads. The underlined letters are used in this Standard: Internal threads G, H Table 6 External threads e, f, g, h Table 6 Designations of Tolerance Grade, Tolerance Position, and Tolerance Class: The tolerance grade is given first followed by the tolerance position, thus: 4g or 5H. To designate the tolerance class the grade and position of the pitch diameter is shown first followed by that for the major diameter in the case of the external thread or that for the minor diameter in the case of the internal thread, thus 4g6g for an external thread and 5H6H for an internal thread. If the two grades and positions are identical, it is not necessary to repeat the sym bols, thus 4g, alone, stands for 4g4g and 5H, alone, stands for 5H5H. Lead and Flank Angle Tolerances: For acceptance of lead and flank angles of product screw threads, see Section 10 of ANSI/ASME B1.13M-2005 (R2015). Short and Long Lengths of Thread Engagement when Gaged with Normal Length Contacts: For short lengths of thread engagement, LE, reduce the pitch diameter tolerance of the external thread by one tolerance grade number. For long lengths of thread engagement, LE, increase the allowance (fundamental deviation) at the pitch diameter of the external thread. Examples of tolerance classes required for normal, short, and long gage length contacts are given in the following table. For lengths of thread engagement classified as normal, short, and long, see Table 7.
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online