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Alpha Thread Gage, Inc.

Mailing address:

  PO Box 261
 

 Royal Oak, MI  

  48068-0261

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Leading the pack in the thread gage industry.

 

PHONE (248) 585-5800 FAX (248) 583-9800

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REFERENCE SHEET

Reference Sheets Available Thread Gage Tolerances- Class Y Tolerances ] Thread Gage Tolerances- Class W Tolerances ] Thread Gage Tolerances- Class X Tolerances ] Metric Thread Gages-Thread Rings & Setting Plugs ] Metric Thread Gages-Thread Work Plugs ] [ American National Taper Pipe Thread Gages-NPT ] Pipe Thread Gages ] Unified Thread Gages- Thread Work Plugs- Pitch Diameter Chart ] Unified Thread Gages- Thread Ring and Setting Plugs ] Gage Pipe Plugs- Internal and External ]

   

American National Taper Pipe Thread Gages (N.P.T)

Illustrations of Internal and External Threads (click here).
FOR GAGING EXTERNAL THREADS-ANPT or NPTF (Illustration)

FOR GAGING INTERNAL THREADS-ANPT or NPTF (Illustration)

BASIC DIMENSIONS N.P.T. TAPER THREAD PLUG AND RING GAGES
Nominal Size of Pipe Threads
per
Inch
Pitch Major Diameters of Plug Gages Pitch Diameters of Plug and Ring Gages Major Diameters of Ring Gages Increase in Diameter per Thread Thick-
ness of THIN  Ring
At Small End At Gaging Notch At Large End Full RIng At Small End At Gaging Notch At Large End, FULL RING At Small End At Gaging Notch
1/16 27 0.03704 0.29289 0.30289 0.30921 0.27118 0.28118 0.28750 0.24947 0.25947 0.00231 0.160
1/8 27 0.3704 0.38522 0.39531 0.40171 0.36351 0.37360 0.38000 0.34180 0.35189 0.00231 0.01615
1/4 18 0.05556 0.51339 0.52763 0.53850 0.47739 0.49163 0.50250 0.44139 0.44563 0.00347 0.2278
3/8 18 0.05556 0.64801 0.66301 0.67350 0.61201 0.62701 0.63750 0.57601 0.59101 0.00347 0.240
1/2 14 0.07143 0.80600 0.82600 0.83936 0.75843 0.77843 0.79179 0.71086 0.73086 0.00446 0.320
3/4 14 0.07143 1.01525 1.03644 1.04936 0.96768 0.98887 1.00179 0.92011 0.94129 0.00446 0.339
1 11.5 0.08696 1.27154 1.29654 1.31422 1.21363 1.23863 1.25630 1.15572 1.18072 0.00543 0.400
1-1/4 11.5 0.08696 1.61504 1.64129 1.65922 1.55713 1.58338 1.60130 1.49922 1.52547 0.00543 0.420
1-1/2 11.5 0.08696 1.85400 1.88025 1.89922 1.79609 1.82234 1.84130 1.73817 1.76442 0.00543 0.420
2 11.5 0.08696 2.32693 2.35418 2.37422 2.26902 2.29627 2.31630 2.21111 2.23836 0.00543 0.436
2-1/2 8 0.12500 2.80278 2.84541 2.87388 2.71953 2.76216 2.79062 2.63628 2.67891 0.00781 0.682
3 8 0.12500 3.42388 3.47175 3.49888 3.34062 3.38850 3.41562 3.25737 3.30525 0.00781 0.766
3-1/2 8 0.12500 3.92075 3.97207 3.99888 3.83750 3.88881 3.91562 3.75425 3.80556 0.00781 0.821
4 8 0.12500 4.41762 4.47038 4.49888 4.33438 4.38712 4.41562 4.25112 4.30387 0.00781 0.844
5 8 0.12500 5.47398 5.53255 5.56188 5.39073 5.449292 5.47862 5.30748 5.36604 0.00781 0.937
6 8 0.12500 6.52935 6.58922 6.62388 6.44609 6.505.97 6.54062 6.36284 6.42275 0.00781 0.958

INTERNAL THREADS For gaging internal internal taper threads, the plug gage is screwed up tight by hand into the internal thread of the product. The thread is within the permissible tolerance when the gaging notch of the working plug gage is not more than 1 turn, large or small, from being flush with the end of the thread.
Click on picture for a larger view.

EXTERNAL THREADS In gaging external taper threads, the ring gage is screwed up tight by hand on external thread of product. The thread is within the permissible tolerance when the gaging face of the working ring gage is not more than 1 turn, large or small, from being flush with the end of the thread.
Click on picture for a larger view.

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