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UNIFIED THREADS OF SPECIAL DIAMETERS,
PITCHES AND LENGTH OF ENGAGEMENT

FED-STD-H28/3(31 MAR 1978) - Thread data are calculated for certain special combinations of diameter and pitch, with pitch diameter tolerances based on a thread engagement length of 9 x Pitch. The pitch diameter limits are applicable for a length of engagement of 5 to 15 times the pitch. (The length of thread on mating parts, however, may exceed the length of engagement by a large amount) These threads are designated by UNS and UNRS. These are included in the Unified Standard Series.

BASIC MAJOR DIAMETER
THREADS PER INCH
LENGTH OF ENGAGEMENT 1D 9Xp 20Xp

LOE
PITCH
H
PDT

EXTERNAL
    MAJOR Ø MAJOR Ø PITCH Ø PITCH Ø  
CLASS ALLOWANCE TOL MAX MIN MAX MIN TOL MINOR Ø
1A
2A
3A
INTERNAL
    MINOR Ø MINOR Ø PITCH Ø PITCH Ø  
CLASS ALLOWANCE TOL MIN MAX MIN MAX TOL MAJOR Ø
1B  
2B  
3B  
 
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