NPT and NPTF Pipe Gage Information

NPTF PIPE GAGES

• NPTF Gages- Are considered "Dry Seal" Pipe Threads.
• NPTF Gages- Are relationship gages.
• NPTF L-1 Tolerance- Plus or minus one turn from the notch on the Plug or Small End Face of the Ring.
• NPTF L-2 Ring or L-3 Plug Tolerance- Plus or minus one half turn from the location of the L-1 gage.
• Crest Check Gage- Will be between one of these sets of Notches; the Notches are in relation to where the L -1 & L-3 of L-2 gages measured.
• MN & MNt
• B & Bt
• MX & MXt

NPTF PIPE PLUGS

NPTF L-1 Plug Gage - Inspects the Pitch Diameter of the Hand Tight L-1 Length of Engagement.

• NPFT L-3 Plug Gage- Inspects the Taper and Wrench Tight L -3 Length of Engagement.
• Crest Check Plug Gage - 6 Step- Inspects the Truncation Limits & Taper of Minor Diameter.

NPTF PIPE RINGS

NPTF L-1 Ring Gage- Inspects the Pitch Diameter of the Hand Tight L-1 Length of Engagement.

• NPTF L-2 Ring Gage- Inspects the Taper and Wrench Tight (L-2) Length of Engagement.
• Crest Check Ring Gage – 6 Step - Inspects the Truncation Limits & Taper of the Major Diameter.
  

NPTF CLASSES OF PRODUCT THREADS

• Class 1 Threads- "Acceptability is determined by coordinated use of L-1 & L2 gages for external product threads and L-1 & L-3 gages for internal product threads. Crest and root truncation is generally considered to be controlled by tooling or other means." (ANSI/ASME B1.20.5).
• Class 2 Threads- Same as above, "however, inspection of root and crest truncation is required," (ANSI/ASME B1.20.3). This means that 6-step Root & Crest Check gages or other methods are required to inspect product root & crest truncation.

NPT PIPE THREADS

• NPT Threads- Are considered "General Purpose" Pipe Threads.
• NPT Threads- Are intend to be sealed at the Crest & Root with Teflon Tape, Pipe Dope, or Other Types of Sealant.
• NPT Threads- Do not require "Crest Check," L-3, or L -2 gages.
• NPT Gages- Made to ANSI/ASME B1.20.1.

NPT PIPE GAGES

• NPT L-1 Plug Gage Tolerance- + or – one turn from the Notch.
• NPT L-1 Ring Gage Tolerance- + or – one turn from the Small End Face of the Ring.