NC Connections - Rotary Shoulder Connection - Thread Plug and Ring Gages - API Spec 7-2

API thread gages
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NC Connections are Rotary Shoulder Connections having the V-040, V050 or V-055 Thread Forms. Gauging practice and thread inspection should conform to the requirements of API Spec 7-2. Thread Check, Inc. offers the complete range of API NC Thread Plug and Ring Gages to API Spec 7-2. Our engineering staff have served on various API gaging subcommittees and have worked in the energy industry for many decades. Thread Check's expert engineers can assist you with engineering and building custom gages. Thread Check is a proud member of the American Petroleum Institute.

Per API Spec 7 - Obsolescence Rotary Shouldered Connections

In 1964, at the API Committee on Drilling and Service Equipment, a new series of rotary shouldered connections was adopted in order to improve the service performance of drill collars and tool joints. 11 of the 13 NC sizes were approved as standard.

For the new style of connections, the size designation is a two digit number indicating the pitch diameter of the pin member at the gage point and the style is referred to as the number style or numbered connection NC. These NC connections utilize a V thread form having a .065 inch flat crest and a .038 inch rounded root. This form is specified as the V-0.038R form. This V .038R form mates with the V-0.065 form that is employed on all API internal flush ( IF ) connections and on the API 4 inch full hole ( FH) connection.

All API IF and FH connections are now considered obsolescent and appear in the appendixes I,J, and K of API specification 7.

Of the new NC connections there are 5 sizes that have the same pitch diameter, taper, pitch, and length of thread as the corresponding size in the IF style and one corresponds to the 4 FH connection.

These 6 connections in the number style can be gauged with the same gauging practice and same gauges required for the equivalent connections.


NC10-PNC10 Thread Plug GageAdd
NC10-RNC10 Thread Ring GageAdd
NC12-PNC12 Thread Plug GageAdd
NC12-RNC12 Thread Ring GageAdd
NC13-PNC13 Thread Plug GageAdd
NC13-RNC13 Thread Ring GageAdd
NC16-PNC16 Thread Plug GageAdd
NC16-RNC16 Thread Ring GageAdd
NC26-PNC26 Thread Plug Gage ( 2 3/8" IF interchangeable )Add
NC26-RNC26 Thread Ring Gage ( 2 3/8" IF interchangeable )Add
NC31-PNC31 Thread Plug Gage ( 2 7/8" IF interchangeable )Add
NC31-RNC31 Thread Ring Gage ( 2 7/8" IF interchangeable )Add
NC35-PNC35 IF Plug GageAdd
NC35-RNC35 IF Ring GageAdd
NC38-PNC38 Thread Plug Gage ( 3 1/2" IF interchangeable )Add
NC38-RNC38 Thread Ring Gage ( 3 1/2" IF interchangeable )Add
NC40-PNC40 IF Plug GageAdd
NC40-RNC40 IF Ring GageAdd
NC44-PNC44 IF Plug GageAdd
NC44-RNC44 IF Ring GageAdd
NC46-PNC46 Thread Plug Gage ( 4" IF interchangeable )Add
NC46-RNC46 Thread Ring Gage ( 4" IF interchangeable )Add
NC50-PNC50 Thread Plug Gage ( 4 1/2" IF interchangeable )Add
NC50-RNC50 Thread Ring Gage ( 4 1/2" IF interchangeable )Add
NC56-PNC56 Thread Plug Gage ( 5" IF interchangeable )Add
NC56-RNC56 Thread Ring Gage ( 5" IF interchangeable )Add
NC61-PNC61 Thread Plug Gage ( 5 1/2" IF interchangeable )Add
NC61-RNC61 Thread Ring Gage ( 5 1/2" IF interchangeable )Add
NC70-PNC70 Thread Plug Gage ( 6 5/8" IF interchangeable )Add
NC70-RNC70 Thread Ring Gage ( 6 5/8" IF interchangeable )Add
NC77-PNC77 IF Plug GageAdd
NC77-RNC77 IF Ring GageAdd
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