Sandvik Coromant Threading - Manual (Page 7)

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1A 1B
2A 2B
3A 3B
¼” 20UNC – 2A
1. Basic in threads
The pitch value is indicated in t.p.i. (threads per inch).
To convert to metric, this should be divided by 25.4 using the
following equation:
20 t.p.i.
 25.4/20 = 1.27 mm.
ISO - unifi ed (UN):
ISO inch threads (UNC, UNF, UNEF, UN)
The UN system has three tolerance classes, ranging from 1
(course) to 3 (fi ne). A typical UN thread is designated as follows:
Tolerance position
Types of UN thread
UNC thread diameter with course pitch
UNF thread diameter with fi ne pitch
UNEF thread diameter with extra-fi ne pitch
UN thread diameter with constant pitch
All of the above types of thread can be created using the UN insert
from Sandvik Coromant
Loose tolerance
Medium tolerance
Tight tolerance
2A – Indicates a medium tolerance
UNC – Indicates a course pitch
20 – Pitch value: threads per inch (t.p.i.)
¼” – Major thread diameter