Typical Tap Designations:

•       Nominal Size:  This is the description of the thread size that tap will make.

•       Thread Form Symbol:  This describes the thread family.

•       Tap Material:  Usually Carbide or HSS

•       Pitch Diameter Limit:  Tells what tolerance thread will be made.

Pitch Diameter Limits (Threads < 1″ in diameter)

L1 = Basic to Basic minus .0005
H1 = Basic to Basic plus .0005
H2 = Basic plus .0005 to Basic plus .0010
H3 = Basic plus .0010 to Basic plus .0015
H4 = Basic plus .0015 to Basic plus .0020
H5 = Basic plus .0020 to Basic plus .0025
H6 = Basic plus .0025 to Basic plus .0030

Thread Form Symbols / Abbreviations

ACME 60° STUB 60° Stub thread form
ACME STUB Stub Acme thread form
ACME-C Acme thread – centralizing
ACME-G Acme thread, general purpose
ANPT Aeronautical National Form taper pipe thread
AWWA American Water Works Association
BA British Association Standard thread form
BSF British Standard Fine thread series
BSPP British Standard Pipe Parallel
BSPT British Standard Pipe Taper
BSW British Standard Whitworth
MM ISO Metric thread form
N BUTT American Buttress screw thread
NC American National Coarse thread series
NEF American National Extra-Fine thread series
NF American National Fine thread series
NGO American National gas outlet threads
NGT American National gas taper threads
NH American National hose & fire hose coupling
NM National Miniature thread series
NPS American Standard straight pipe thread
NPSC American Standard straight pipe thread in couplings
NPSF American Standard internal straight pipe thread (dryseal)
NPSH American Standard straight pipe thread for hose couplings & nipples
NPSI American Standard intermediate straight pipe thread (dryseal)
NPSL American Standard straight pipe thread for locknuts
NPSM American Standard straight pipe thread for mechanical joints
NPT American Standard taper pipe thread
NPTF Dryseal American Standard taper pipe thread
NPTR American Standard taper pipe thread for rail fittings
NS Special threads of American National Form
PTF Dryseal SAE Short Taper pipe thread
SGT Special Gas Taper thread form
SPL-PTF Dryseal Short Taper Pipe thread
STI Special Threads for Helical Coil Wire Screw Thread Inserts
UN Unified and American thread series
UNC Unified and American Coarse thread series
UNEF Unified and American Extra-Fine thread series
UNF Unified and American Fine thread series
UNIV Unified Miniature Thread Series
UNJ Unified Thread Series with Controlled Root Radius
UNJC Unified Coarse Thread Series with Controlled Root Radius
UNJF Unified Fine Thread Series with Controlled Root Radius
UNR Unified Constant Pitch thread series with Controlled Root Radius
UNRC Unified Coarse Thread Series with Controlled Root Radius
UNRF Unified Fine Thread Series with Controlled Root Radius
UNS Unified and American threads of selected special diameters and pitches