NPTF

N.P.T.F.
SizeThreads per inchPlug GageRing Gage
Basic L-1Basic L-33-Step L-13-Step L-36-Step PlainL-1L-26-Step Plain
1/16"27P006227NL1KP006227NL3KP006227NL1-3KP006227NL3-3KP006227N6KT006227NL1KT006227NL2KT006227N6K
1/8"27P012527NL1KP012527NL3KP012527NL1-3KP012527NL3-3KP012527N6KT012527NL1KT012527NL2KT012527N6K
1/4"18P025018NL1KP025018NL3KP025018NL1-3KP025018NL3-3KP025018N6KT025018NL1KT025018NL2KT025018N6K
3/8"18P037518NL1KP037518NL3KP037518NL1-3KP037518NL3-3KP037518N6KT037518NL1KT037518NL2KT037518N6K
1/2"14P050014NL1KP050014NL3KP050014NL1-3KP050014NL3-3KP050014N6KT050014NL1KT050014NL2KT050014N6K
3/4"14P075014NL1KP075014NL3KP075014NL1-3KP075014NL3-3KP075014N6KT075014NL1KT075014NL2KT075014N6K
1"11-1/2P100099NL1KP100099NL3KP100099NL1-3KP100099NL3-3KP100099N6KT100099NL1KT100099NL2KT100099N6K
1 1/4"11-1/2P125099NL1KP125099NL3KP125099NL1-3KP125099NL3-3KP125099N6KT125099NL1KT125099NL2KT125099N6K
1 1/2"11-1/2P150099NL1KP150099NL3KP150099NL1-3KP150099NL3-3KP150099N6KT150099NL1KT150099NL2KT150099N6K
2"11-1/2P200099NL1KP200099NL3KP200099NL1-3KP200099NL3-3KP200099N6KT200099NL1KT200099NL2KT200099N6K
2 1/2"8P250008NL1KP250008NL3KP250008NL1-3KP250008NL3-3KP250008N6KT250008NL1KT250008NL2KT250008N6K
3"8P300008NL1KP300008NL3KP300008NL1-3KP300008NL3-3KP300008N6KT300008NL2KT300008N6KT300008N6K

National Pipe Taper Dryseal Pressure-Tight Joints

Dryseal pipe threads are designed to seal pressure tight joints without the use of sealing compounds, therefore a greater variety of gages and/or measuring equipment is used to more adequately check size, taper and thread form. L1 and L3 Plugs supplied with 1 step as standard.

In gaging internal threads with N.P.T.F. plug gages, there are three gaging members involved:
(1) L-1 thread plug gage which checks the thread elements within hand tight engagement
(2) L-3 thread plug which checks the threads that will be engaged when wrench tight
(3) 6-Step plain plug which is used to check the minor diameter of the female fitting.

In gaging external threads with N.P.T.F. ring gages, there are three gages employed:
(1) 6-Step plain ring which checks the major diameter of the male fitting
(2) L-1 (thin) ring which checks the thread elements over the distance of hand tight engagement
(3) L-2 (thick) ring which checks the thread elements of those threads engaged when wrench tight. A.N.P.T. and N.P.T.F. are not meant to be interchangeable.

N.P.T.F. Internal taper pipe threads may be gaged in the same manner as the A.N.P.T. threads. Gages are dimensionally different, however, and must not be interchanged. The turns method may be substituted for the “standoff” method to compensate for gage and product chamfers. With the turns method, the number of turns are counted from hand tight engagement to complete release, and the gaging steps are completely disregarded. A tolerance of plus or minus one turn is permitted from the basic number of turns specified. As a check on taper, the difference in turns between the L-1 and L-3 plugs shall be within one-half turn of the difference between the basic turns engagement of the plug gages. Truncation must be within the proper limits on a six-step dryseal plain taper plug gage.

N.P.T.F. External taper pipe threads are checked in the same manner as A.N.P.T. threads. Gages are dimensionally different, however, and must not be interchanged. The turns method may be substituted for the “standoff” method to compensate for gage and product chamfers. A tolerance of plus or minus one turn is permitted from the basic number of turns specified. As a check on taper, the difference in turns engagement with the L-1 and L-2 dryseal rings shall be within one-half turn of the difference between the basic turns engagement of the ring gages.

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