• Home
  • Download PDF
  • Order CD-ROM
  • Order in Print

Home > Ordnance Documents and other related manuals > > Thread Designations
Thread Fit And Designations.
Figure 42. Thread Cutting Gages.

Lathe Operations
Page Navigation
  105    106    107    108    109  110  111    112    113    114    115  

LATHE OPERATIONS - OD1645 - LESSON 1/TASK 3
2 Class 2 Fit.
This fit represents a high quality of commercial
thread product, and is interchangeable screw thread work.
3 Class 3 Fit.  This fit represents an exceptional high quality of
commercially threaded product and is recommended only in cases where the
high cost of precision tools and continual checking are warranted.
4 Class  4  Fit.
This  fit  is  intended  to  meet  very  unusual
requirements more exacting than those for which class 3 is intended.  It is
a selective fit if the initial assembly by hand is required.  It is not, as
yet, adaptable to quantity production.
(2) Thread Designations.
In general, screw thread designations give the
screw number (or diameter) first, then the initial letter of the series, NC
(National coarse), UNF (Unified fine), NS (National special), etc., followed
by the class of fit.  If a thread is a left-hand, the letters LH follow the
fit.  An example of designations is as follows:
Major diameter of thread
.
Number of threads per inch
.
.
Thread series symbols
.
.
.
Class of thread .
.
.
.
.
.----External thread
.
.
.
.
.
Left-hand
.
.
.
.
.
.
3/4 10  UNC 2
A
LH
Two samples and explanations of thread designations are as follows:
(a) No. 12 (0.216) --24 NC-3.  This is a number 12 (0.216 inch diameter)
thread, 24 National coarse threads per inch, and a Class 3 fit.
(b) 1/4-28UNF-2A LH.
This is a 1/4 inch diameter thread, 28 Unified
fine threads per inch, left hand thread, and a Class 2A fit.
e.
Thread Cutter Bits and Cutters.
(1) The basic forms of thread cutting bits and cutters were given in the
first part of the lesson.
110






Western Governors University

< Previous Page
Index ^
Next Page >

Privacy Statement
Press Release
Contact

© Copyright Integrated Publishing, Inc.. All Rights Reserved. Design by Strategico.