10
11
l However, in some standards like : BSP, NPT,
NPTF, and PG, the diameter value which
appears in designation is not the nominal
diameter. For the right values you must refer
to a conversion table
l Example: 1/2” x 14BSP
Nominal Diameter = 0.825”
August 2006
Conversion table sample for BSP:
BSP
Threads Length of
Major
Nominal Size per Inch Engagement Diameter Min.
1/8
3/8
0.3830
28
1/4
1/2
0.5180
19
3/8
1/2
0.6560
19
1/2
5/6
0.8250
14
5/8
5/8
0.9020
14
3/4
3/4
1.0410
14
7/8
3/4
1.1890
14
You can find the conversion table for BSP in the
TM Gen and TT Gen
Small UN threads are not defined by thread value
l Standard UN threads smaller than 1/4” are
defined by SIZE NUMBER and not by the
real thread value
Example: 12-24 UNC > major diameter=0.2160”
l You can find the conversion table in the
TM Gen and TT Gen
13
Threading Tips
Thread designation and thread nominal diameter can
be different
l Normally the diameter which appears in the
thread designation is the nominal (major) diameter
Example: M10 x 1.5
Nominal Diameter = 10mm
12
Making Threading Easy
Nominal Size
Major dia. (Inch)
Major dia. (mm)
10-56 UNS
12-24 UNC
12-28 UNF
12-32 UNEF
12-36 UNS
12-40 UNS
12-48 UNS
12-56 UNS
1/4”-20 UNC
0.1900
0.2160
0.2160
0.2160
0.2160
0.2160
0.2160
0.2160
0.2500
4.8260
5.4864
5.4864
5.4864
5.4864
5.4864
5.4864
5.4864
6.3500
What is the difference between UNC, UNF and UNEF ?
l The difference between the 3 standards is in the l For a given pitch: UNC, UNF, UNEF have exactly
ratio between the thread diameter and pitch size
the same profile (see picture below) but different
ratio between diameter and pitch
l UNC (Coarse pitch)- relatively small diameter
with large pitch
Internal
1/4P
UNF (Fine pitch)- large diameter with same pitch
60°
UNEF (Extra fine pitch)- relatively big diameter
for same pitch
h
Example: 5/16” x 18 UNC
9/16” x 18 UNF
111/16” x 18 UNEF
1/8P
External
UNC, UNF, UNEF
all have the same profile
For tool selection and cutting data in Thread
Turning applications use our TT Gen.
For the best Thread Milling CNC Programming,
use VARDEX TM Gen software utilities.
For free copies, go to www.vargus.com
Now available in 10 languages!!!
All issues of the VARDEX Tips are available on the VARGUS website: www.vargus.com
© All rights reserved, VARGUS Ltd. 2006