NPT Thread Gages - Judge Tool & Gage Inc.

1 - 14 -Gaging of NPT threads is quite easy and differs from straight threads in that only one gage , an L1 plug or L1 ring is used to taper pipe Thread plug has a step at the L1 distance from its small end. When turned hand tight into the product sinternal pipe Thread , (do not force the gage ), the step is required to be flush with the large end of the product Thread within a toleranceof plus or minus one turn. Many times the product Thread is chamfered, countersunk or recessed, exceeding the major diameter of thethread. In these instances, the gaging point of the product Thread becomes where the first visible sign of a scratch mark at the majordiameter occurs on the chamfer taper pipe Thread ring gage has a thickness equal to the L1 ring s large end (marked face) is turned hand tight onto theexternal pipe Thread until it stops (do not force the gage ). The small end of the ring gage is required to be flush with the small end ofthe pipe within a tolerance of plus or minus one of PipeThreadsPer InchMajor DiametersPitch DiametersMinor DiametersBasic L1 LengthAt Small EndAt Gaging NotchAt Large EndAt Small EndAt Gaging NotchAt Large EndAt Small EndAt Gaging Notch1 1 1/411 1 1/211 1 1 1 1 +/- 1 turnBasic NotchL1 Plug gage - NPTL1 Ring GageNPTF lush with small end face of gage +/- 1 Quantity2.

2 Nominal Size & Threads Per Short or Long Form Certification if Ordering Pipe Gages Please Specify:NPT Thread GagesFitting- 15 - Gages Required to check other Pipe ThreadsType of ThreadInternal Product ThreadsExternal Product ThreadsPTF SAE ShortPTF SAE Short L1 & L3 Plug GagesPTF SAE Short L1 & L2 Ring GagesANPTANPT L1, L3 & Plain 6-Step Plug Gages ANPT L1, L2 & Plain 6-Step Ring GagesNPSFNPTF L1 Plug GageMates with NPTF External ThreadsNPSMGo & Not Go Plug GagesGo & Not Go Ring GagesNPSLGo & Not Go Plug GagesGo & Not Go Ring GagesNHGo & Not Go Plug GagesGo & Not Go Ring GagesNPSHGo & Not Go Plug GagesGo & Not Go Ring GagesNPSCNPT L1 Plug GageMates with NPT External ThreadsBSPT System ABSPT Thread PlugBSPT Thread RingBSPT System BBSPT Thread Plug & Plain PlugBSPT Thread Ring & Plain RingBSPPGo & Not Go Thread PlugGo & Not Go Thread RingsJIS (Japanese) & DIN (German) Parallel and Tapered Pipe Thread Gages are also PlugL3 PlugCrest Check PlugScrew the L3 plug into thefitting (hand tighten).

3 Thegage must match the classifi-cation of the L1 plug within+/- 1/2 the L1 plug into thefitting (hand tighten). Thisclassifies the Thread as to Maximum , Basic , or Minimum .Insert 6-step Crest Checkplug into the fitting. Whenthe L1 plug is at the maxi-mum notch, the 6-step gagemust go between MX and MXT notch. When the L1plug is at the Basic Notch,the 6-Step gage must go be-tween B and BT the L1 plug is at mini-mum notch, the 6-Step gagemust go between the MN and MNT Use of NPTF 3-Step & 6-Step Gages - 16 -Class 1 ThreadsGaging of NPTF class 1 threads is identical to that of NPT threads with the use of the L1 plug or L1 ring. In addition, the use of an L3 plug or L2 ring is necessary fora functional check of taper deviations and continuation of Thread beyond the L1 length of L3 plug or L2 ring may not vary from the relative position established by the L1 plug or ring by more than 1/2 turn.

4 Crest and root truncations are generallyconsidered adequately controlled by the tooling used to produce the product threads in NPTF class 1 2 ThreadsGaging of NPTF class 2 threads is identical to that of NPTF class 1 threads with the use of L1 and L3 plugs or L1 and L2 rings. The L1 plug or L1 ring is also used toclassify the Thread as being maximum , basic or minimum . (see diagram) Note: Basic range is 1/3 turn from basic step. The use of 4-Step L1 gagesfacilitates classification of product threads. They offer 2 steps for each classification range rather than estimating the range by turning the gage from the basic stepand are highly recommended. NPTF class 2 threads also require the measurement or gaging of the crests and roots of the threads. While direct measurements or optical projection is moreaccurate and should be considered the final method in the event of a dispute, 6-Step crest and root truncation Gages offer fast, simplified and acceptable method ofchecking crests and roots.

5 The 6-Step Gages consist of 3 pairs of steps, each pair corresponding to the classification of the Thread established by the L1 plug or ringas maximum , basic , or minimum. Specifications for all Class 2 NPTF threads are shown for the recommended 4-Step gage design on the following : For NPTF threads: T=2 Turns For PTF-SAE Short, NPSF and NPSI threads: T= TurnsClassification of Product Thread Size Using 4-Step Steps of the crest check or root check are marked and correspond to the following:MN Minimum Thread with minimum truncation. MNT Minimum Thread with maximum truncation. B Basic Thread with minimum truncation. BT Basic Thread with maximum Maximum Thread with minimum truncation. MXT Maximum Thread with maximum Quantity2. Nominal Size & Threads Per Basic, 3-Step, or 4-Step design on L1, L3 plugs & L1, L2 Rings. (Basic unless otherwise specified.)

6 4. Single or Double Ended plug Short or Long Form Certification if Ordering Please Specify:NPTF Thread GagesStep 1 Step 2 BasicStep(REF)Step 3 Step 4 MinimumRangeInternalBasicRangeMaximum Range InternalMaximum RangeExternal(Basic Thread )Minimum RangeExternalT/3T/3T/3T- 17 -NPTF Class 2 SpecificationsNominalSize & Dimensions for Crest Check Plug GagesBasic Dimensions for Root Check Plug GagesMax. Dia At L3 Basic Thread with Max. Pipe ThreadMin. ThreadMax. ThreadMax. Dia. at L1 + L3 length from end of fitting. Basic Thread with Min. width of crest at Major Pipe ThreadMin. ThreadMax. +.00015+.000+.000+.000+.0002+.002+.002+. +/- . + + + + + Dimensions for L1 Ring GagesBasic Dimensions for L2 Ring GagesNominal Size & EndMaximum RangeBasic RangeMinimum RangeBasicLengthL2 Large EndMaximum RangeBasic RangeMinimum 1 Step 2 Step 2 Step 3 Step 3 Step 4 Step 1 Step 2 Step 2 Step 3 Step 3 Step 4(L1 - p)(L1 - 1/3p) (L1 - 1/3p) (L1 + 1/3p)(L1 + 1/3p)(L1 + p)L2-pL2-1/3p L2-1/3p L2+1/3p L2+1/3pL2+p1.

7 Dimensions for Crest Check Ring GagesBasic Dimensions for Root Check Ring GagesNominal Size & Diam at L2 Basic Thread with DBasic Pipe ThreadMinimum Thread Maximum Dia. at L2 length from end of pipe. Basic Thread with min. truncation of Crest at MinorDia. FBasic Pipe ThreadMin. ThreadMax. ThreadMinTrunc. +.000+.000+.000+.0002+.002+.002+.002+.00 00+/- . +/- . +/- . + + + + Size & Dimensions for L1 Plug Gages , NPTFB asic Dimensions for L3 Plug GagesBasicLengthL1 Small EndBasic Dim. at L1 PlaneMin. RangeBasic RangeMax. RangeBasicLengthL1+L3 Small EndFourThreadsL3+pMin. RangeBasic RangeMax. RangePitch Dia. Major Dia 1 Step 2 Step 2 Step 3 Step 3 Step 4 Step 1 Step 2 Step 2 Step 3 Step 3 Step 4L1-pL1-1/3pL1-1/3pL1+1/3pL1+1/3pL1+pL1+ L3-pL1+L3-1/3p L1+L3-1/3p L1+L3+1/3pL1+L3+1/3pL1+L3+p1