Sandvik Coromant Threading - Manual (Page 4)

4
1. Basic in threads
Threading terms and defi nitions
1. Root/bottom
The bottom surface joining the two adjacent fl anks of
the thread
2. Flank/side
The side of a thread surface connecting the crest and
the root
3. Crest/top
The top surface joining the two sides, or fl anks.
P = Pitch, mm or threads per inch (t.p.i.)
= The profi le angle
= The helix angle of the thread
d / D = The major diameter, external/internal
d
1
/ D
1
= The minor diameter, external/internal
d
2
/ D
2
= The pitch diameter, external/internal
Pitch diameter, d
2
/ D
2
This is the effective diameter of the screw
thread; approximately half way between the
major and minor diameters.
Helix angle
The helix angle (
)is the geometrical shape
of the screw thread, it is based on the pitch
diameter of the thread (d
2
, D
2
), and the
pitch (P) – the distance from one point on a
thread profi le to the corresponding point on
the next.
This measurement can be represented by
a triangle being unwound from the compo-
nent.
The same pitch on different dia-
meters gives a different helix angle,
see example above.