This standard specifies the common terms and definitions of threads. This standard applies to all kinds of threads. GB/T 14791-1993 Thread Terminology GB/T14791-1993 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Terms of screw threads
The terms of screw threads
1 Subject content and scope of application
This standard specifies the common terms and definitions of screw threads. This standard applies to all kinds of screw threads.
2 General terms
GB/T 14791--93
Replaces GB 2515-81
2.1 Helix
The trajectory of a point moving along the surface of a cylinder or cone, the axial displacement of the point and the corresponding angular displacement are in a constant ratio (see Figure 1). Development surface
Development surface
2.2 Screw thread
On the surface of a cylinder or cone, a continuous protrusion with a specified tooth shape formed along the helix (see Figures 2 and 3). Note: The protrusion refers to the solid part between the two sides of the thread, also known as the tooth. Approved by the State Administration of Technical Supervision on December 28, 1993 and implemented on October 1, 1994
2.3 Parallel screw threadGB/T14791-93
Threads formed on the surface of a cylinder [see Figure 2(a), Figure 3(a)]. 2.4 Taper screw threadThreads formed on the surface of a cone [see Figure 2(b), Figure 3(b)]. 2.5 External threadExternal thread
Threads formed on the outer surface of a cylinder or cone (see Figure 2). 2.6 Internal threadInternal thread
Threads formed on the inner surface of a cylinder or cone (see Figure 3). 2.7
Screw thread pair
The connection formed by the mutual screwing of internal and external threads. 2.8 Single-start threadThreads formed along a spiral line (see Figure 4). (b)
GB/T14791—93
2.9 Multi-start thread A thread formed along two or more helical lines, which are equally spaced in the axial direction (see Figure 5). Figure 5
2.10 Right-hand thread A thread screwed in when rotating clockwise (see Figure 6). 2.11 Left-hand thread A thread screwed in when rotating counterclockwise (see Figure 7). Figure 6
2.12 Complete thread
completethread
A thread with complete shape at both the crest and root (see Figure 25). 2.13 Incomplete thread GB/T 14791-93
A thread with complete root and incomplete crest (see Figure 25). 2.14
Washout thread;vanish thread A thread with incomplete root that transitions to a smooth surface (see Figure 25). 2.15 Useful thread
A thread consisting of a complete thread and an incomplete thread, excluding the screw tail (see Figure 25). 3 Geometric elements and parameter terms
3.1 Tooth form and related terms
3.1.1 Thread tooth form
The outline shape of the thread on the plane passing through the thread axis. 3.1.2
Fundamental triangle The triangle that forms the thread tooth form, whose base is parallel to the generatrix of the pitch diameter cylinder or pitch diameter cone (see Figure 8). Fundamental triangle
Fundamental flange angle
In the figure: α/2-
flank angle;
H——fundamental triangle height.
3.1.3 Fundamental triangle heightThe distance from the vertex of the fundamental triangle to its base along the direction perpendicular to the thread axis (see Figure 8). 3.1.4 Basic profile
The theoretical profile common to both internal and external threads formed by cutting off the top and bottom of the original triangle. It is the basis for determining the design profile of the thread (see Figure 9).
3.1.5 Depth of truncation The distance from the top or bottom of the thread profile to the vertex of the original triangle in the direction perpendicular to the thread axis (see Figure 9).
3.1.6 Design profile
The design profile specifies the various clearances and circular radii required for the function relative to the basic profile. It is the starting point for the basic deviation of internal and external threads (see Figure 10).
GB/T14791—93
3.1.7 Maximum material profile90
The thread profile in the maximum material state determined by the design profile and the basic deviations and tolerances of each diameter. 3.1.8 Minimum material profile The thread profile in the minimum material state determined by the design profile and the basic deviations and tolerances of each diameter. 3.1.9 Crest The thread surface connecting two adjacent flanks at the top of the thread protrusion (see Figure 11). Root The thread surface connecting two adjacent flanks at the bottom of the thread groove (see Figure 11). 3.1.11 Flank The portion of the spiral surface between the crest and the root on a section through the thread axis (see Figure 11). Drawing Tanyu #
In the figure: P—pitch.
3.2 Diameter and related terms
3.2.1 Nominal diameter The diameter of the thread size.
Note: Pipe threads are represented by size codes.
3.2.2 Major diameter
GB/T 14791—93
Pitch line
The diameter of an imaginary cylinder or cone tangent to the external thread crest or internal thread root (see Figures 17 and 18). 3.2.3 Minor diameter
The diameter of an imaginary cylinder or cone tangent to the external thread root or internal thread crest (see Figures 17 and 18). 3.2.4 Crest diameter
The diameter of an imaginary cylinder or cone tangent to the external thread crest or internal thread crest, i.e. the major diameter of the external thread or the minor diameter of the internal thread (see Figures 17 and 18).
3.2.5 Root diameter
The diameter of an imaginary cylinder or cone tangent to the root of an external or internal thread, i.e., the minor diameter of an external thread or the major diameter of an internal thread (see Figures 17 and 18).
3.2.6 Pitch diameter
The diameter of an imaginary cylinder or cone whose generatrix passes through the place where the widths of the groove and the protrusion on the tooth profile are equal. This imaginary cylinder or cone is called a pitch cylinder or a pitch cone (see Figures 17 and 18). P/2 P/2
Pitch line
3.1.21 Flank angle
GB/T 14791-93
On the thread tooth profile, the angle between the tooth flank and the perpendicular to the thread axis (see Figure 15). Sub-items
In the figure: α—
a tooth profile angle;
α/2—
a tooth profile half angle.
In the figure: α1~α2——tooth side angle;
tooth profile angle.
3.1.22 radius of rounded crest radius of the rounded crest part of the tooth top (see Figure 16). radius of rounded root3.1.23
radius of the rounded part of the tooth bottom (see Figure 16). In the figure: P—pitch
3.2.7 Simple pitch diameter GB/T14791--93
Thread axis
Continued Figure 18
Pitch line
The diameter of an imaginary cylinder or cone, the generatrix of which passes through the place where the groove width on the tooth profile is equal to 1/2 of the basic pitch (see Figure 19). bzxz.net
(P-4P)/2
In the figure: P-
Pitch;
Pitch error
3.2.8 Virtual pitch diameter (P-AP)/2
The pitch diameter of an imaginary thread that just contains the actual thread within the specified screwing length. This imaginary thread has an ideal pitch, half angle and tooth profile height, and a gap is left at the top and bottom of the tooth to ensure that it does not interfere with the major and minor diameters of the actual thread when contained (see Figure 20).
Pitch.
In the figure, P
GB/T 14791-93
Explosion axis
Continued Figure 17
Medium diameter line
Medium diameter line
In the figure: Ph-—lead;
dz—medium diameter;
$thread lead angle.
4 Fit and related terms
GB/T14791--93
4.1 Depth of thread engagement The distance between the overlapping parts of the tooth sides of two mating threads in the direction perpendicular to the thread axis (see Figure 23). Thread engagement
4.2 Major clearance
The radial distance between the root of the internal thread and the crest of the external thread in the designed tooth profile (see Figure 10). 4.3 Minor clearance The radial distance between the crest of the internal thread and the root of the external thread in the designed tooth profile (see Figure 10). 4.4 Length of thread engagement The length of the part of two mating threads that are engaged with each other along the thread axis (see Figure 24). 3.2.9 Gauge diameter GB/T14791—93 The basic major diameter of the internal or external taper thread given in the design (see Figure 25). Axis of thread Axis of pitch cylinder or pitch cone (see Figures 17 and 18). Pitch line Pitch line The generatrix of the pitch cylinder or pitch cone (see Figures 17 and 18). 3.3 Pitch and related terms 3.3.1 Pitch The axial distance between two points corresponding to the pitch line of two adjacent teeth (see Figure 21). 3.3.2 Lead The axial distance between two points corresponding to the pitch line of two adjacent teeth on the same helical line (see Figure 1). Double thread In the figure: P pitch; Ph lead.
3.3.3 Lead angle leadangle The angle between the tangent of the helix and the plane perpendicular to the axis of the thread on a mid-diameter cylinder or mid-diameter cone (see Figure 22). Thread ridge thickness thread ridge thickness3.3.4
The axial distance between the two sides of a thread protrusion on the mid-diameter line on the thread tooth profile (see Figure 16). 3.3.5 Thread groovewidth The axial distance between the two sides of a thread groove on the mid-diameter line on the thread tooth profile (see Figure 16). Value (see Figure 26).
Deviation in lead
The actual value of the lead is the difference between its basic value. GB/T 14791—93
Cumulative error in lead5.5
Within the specified thread length, the maximum absolute value of the difference between the actual axial distance between any two tooth flanks and the intersection of the mid-diameter line on the same helical surface and its basic value (see Figure 27).
In the figure: AP:
In the figure: △Phi-
Pitch deviation;
Cumulative pitch error.
Lead deviation;
Cumulative lead error.
5.6 Helix error in the axisThe maximum variation of the actual helix line from its ideal helix line along the axial direction within the specified length. Deviation of flank angle5.7
The difference between the actual value of the flank angle and its basic value. 5.8 Pitch diameter equivalent of error in pitch The pitch error is converted into the value of the pitch diameter.8 Pitch diameter equivalent of error in pitch
pitch diameter equivalent of error in pitch The pitch error is converted into the value of the pitch diameter.8 Pitch diameter equivalent of error in pitch
pitch diameter equivalent of error in pitch The pitch error is converted into the value of the pitch diameter.
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