Post by b***@aol.comPost by DrFryeI am doing and inventory of our thread gages and have come across several
odd gages. They have a -2 on the end of the size. For example: 1 1/8-12
NF-2. It's on the GO and the NO-GO ring. The pitch diameter is slightly
larger on these -2 ring gages than on the standard gages. Couldn't find any
info in the Machinery Handbook. Can anyone explain these?
NF stands for National Fine also called UNF Unified National Fine So
my guess is your 1 1/8-12 UN-2 is the same as 1.125-12 UNF-2A.
http://www.eng-tips.com/viewthread.cfm?qid=216916&page=6
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Reference Specifications:
ANSI B1.1-1989 Unified Inch Screw Threads (UN and UNR Thread Form)
FED-STD-H28A Notice 1 dated 09/10/01 Screw-Thread Standards for Federal
Services
The term "NS" is derived as American National-Special.
Per FED-STD-H28, American National threads are obsolete and are carried over to
the Unified series.
Per H28:
Replacements for obsolete American National thread classes
American National class 1 coarse thread sizes (NC-1) is approximately equivalent
to Unified class 1A/1B series. Class 1 fine thread series (NF-1) is
approximately equivalent dimensionally to Unified class 2A/2B series. Standard
Unified series threads should be considered prior to approval or replacement by
non-standard threads.
American National class 2 coarse thread sizes (NC-2). 8 thread series (8N-2), 12
thread series (12N-2), 16 thread series (16N-2), and extra fine thread series
(NEF-2) are most nearly equivalent to Unified series UNC-2A/2B, 8UN-2A/2B,
12UN-2A/2B, 16UN-2A/2B and UNEF-2A/2B, respectively. Class 2 fine thread series
(NF-2) is approximately equivalent dimensionally to Unified class 3A/3B series,
but the use of class 2A/2B series should be considered prior to approval of
replacement by class 3A/3B.
]
Post by b***@aol.comIf the PD is not within 2A tolerance for each member then the gauge is
out of tolerance or it is a mislabeled special.