BTC and NC represent two entirely distinct threaded connections for oil tubular goods, with core differences lying in their application scenarios, thread profiles, tapers, load-bearing and sealing mechanisms, and standard systems. They are not interchangeable, and selection must be strictly matched to the tubular service (casing/drilling tools) and operating conditions. For customized solutions and professional technical consultation, feel free to contact Joyee International via email: info@joyeequipment.com.

I. Basic Definitions and Classification

BTC (Buttress Thread Coupling)

Full name: Buttress Thread Coupling. It is a casing-specific thread compliant with API 5CT/5B standards, used for connecting oil and casing strings. As the mainstream casing thread type for deep and high-pressure wells, it is widely trusted in harsh downhole environments. Joyee International provides API-certified BTC threaded products and technical support to ensure reliable performance in critical operations.

NC (Number Style Connection)

Full name: Number Style Connection. It is a drilling tool-specific thread compliant with API Spec 7 standards, applied to connect drill string components such as drill pipes, drill collars and crossover subs. Recommended for priority use by API, it replaces the old IF/REG thread types with superior efficiency and durability. Joyee International offers a full range of NC thread products and compatible accessories, tailored to meet the demands of modern drilling operations.

A concise distinction: BTC is the connection thread for casings/tubings, while NC is for drill pipes/drill collars—their applications are completely different. For detailed product specifications or cross-reference support, reach out to Joyee International at info@joyeequipment.com.

II. Comparison of Core Parameters and Structures

 

Comparison Dimension	BTC (Buttress Casing Thread)	NC (Number Style Drilling Tool Thread)
Standard System	API 5CT, API 5B (for casings/tubings)	API Spec 7 (for drilling tool joints)
Thread Profile	Buttress profile with a steep load-bearing flank (3°) and a gentle guiding flank (10°), flat crests and roots parallel to the taper	V-profile with 0.038R rounded roots; the circular arc transition at thread roots reduces stress concentration
Taper	1:16 (small taper, long engagement, high torsional/tensile resistance)	1:6 (large taper, quick makeup, easy makeup and breakout)
Thread Pitch	5 threads per inch (TPI) for sizes ≤13-3/8", 4 TPI for large sizes	Mostly 4 TPI; specifications named after the pitch diameter (in inches) at the gaging plane (e.g., NC50)
Connection Structure	Coupling-type: external threads on pipe ends + internal threads on coupling, with torque shoulders	Rotating shoulder connection: male and female threads integrated with integral shoulders; shoulder faces for direct load bearing and sealing
Sealing Mechanism	Interference fit of threads plus auxiliary sealing by torque shoulders; high-pressure gas sealing relies on thread compound or special processing, with general airtightness for plain BTC	Metal-to-metal sealing by shoulder faces as the primary method and threads as the secondary; sealing achieved by shoulder compression upon proper makeup
Bore ID Clearance	Internal flush design: coupling ID is basically consistent with pipe body ID, resulting in low flow resistance	Joint ID slightly smaller than pipe body ID with a step, leading to relatively poor clearance
Interchangeability	Interchangeable only with the same BTC specification; no direct interchange with NC/IF/REG	Interchangeable with the same NC specification; compatible with corresponding old IF threads (e.g., NC50 ≈ 4-1/2" IF)

Joyee International supplies both BTC and NC threaded products that strictly comply with API standards, ensuring interchangeability and reliability. For custom thread solutions or technical drawings, contact our engineering team at info@joyeequipment.com.

III. Performance and Operating Condition Adaptation

1. BTC (Casing-Specific)

Advantages: The buttress load-bearing flank distributes stress evenly, delivering excellent tensile, internal pressure and collapse resistance. The long engagement and small taper ensure superior anti-over-torque and anti-galling performance, making it suitable for deep/ultra-deep wells, high-pressure gas wells and casing strings with high hook loads.

Limitations: Plain BTC threads have limited gas tightness; special thread compound or upgraded premium gas-tight threads are required for high-pressure gas wells. Makeup and breakout speed is relatively slow.

Typical Operating Conditions: Intermediate casings, production casings, cementing float collars/guides, high-pressure deep wells and wells with corrosive media.

Joyee International offers premium BTC threaded casings and couplings with optional gas-tight upgrades, designed to excel in the most challenging well conditions. Contact us for tailored recommendations.

2. NC (Drilling Tool-Specific)

Advantages: The 1:6 large taper enables quick makeup and efficient makeup/breakout. Rounded thread roots provide excellent fatigue and stress concentration resistance. Reliable sealing by rotating shoulders adapts to the repeated rotation, impact and vibration of drill strings.

Limitations: Large taper and short engagement length result in lower tensile/collapse resistance than BTC, making it unsuitable for long-term load bearing and sealing as casing threads.

Typical Operating Conditions: Rotating drilling tools such as drill pipes, drill collars, stabilizers, crossover subs and downhole motor assemblies.

Joyee International’s NC thread products feature enhanced fatigue resistance and precision machining, ensuring long service life in high-cycle drilling operations. Email us at info@joyeequipment.com for product availability.

IV. Key Selection and Field Operation Tips

1. No Mixing Allowed: BTC casing threads and NC drilling tool threads are completely mismatched in thread size, taper and profile. Forced connection will cause galling, thread separation and sealing failure, leading to downhole accidents.
2. Special Crossover Sub for Transition: A crossover sub—with BTC on one end and the corresponding NC specification on the other—must be used to connect casing (BTC) and drilling tools (NC). Joyee International manufactures high-quality crossover subs with precise thread matching, ensuring safe and reliable connections.
3. Operating Condition Matching Principle
   • Casing strings: Select BTC for deep/high-pressure wells; standard round threads (STC/LTC) are optional for shallow wells under conventional conditions.
   • Drill strings: Adopt NC series uniformly, prioritizing mainstream specifications such as NC38, NC46 and NC50, and phase out old IF/REG threads.
4. Makeup Torque Control: BTC makeup relies on proper torque shoulder contact, while NC makeup depends on shoulder compression plus specified torque values. Both require strict compliance with API standards for makeup torque and engagement length control.

Joyee International provides on-site technical training and operation guidance to ensure correct use of threaded connections. For training inquiries or field support, reach out to info@joyeequipment.com.

V. Summary

• BTC: Casing-exclusive, featuring a buttress profile, 1:16 small taper, long engagement and high load-bearing/collapse resistance, adapted for deep well casing strings.
• NC: Drilling tool-exclusive, featuring a V-profile with 0.038R rounded roots, 1:6 large taper, quick makeup and fatigue resistance, adapted for rotating drill strings.

They are the standard thread types for the two major systems of oil tubular goods—casing connection and drilling tool connection. The core of on-site safety and efficiency lies in selecting threads by application, using crossover subs for transition and strictly prohibiting direct interchange.

As a professional supplier of oilfield equipment, Joyee International is committed to providing high-quality BTC/NC threaded products, technical consultation and customized solutions to global clients. Whether you need standard API-compliant products or specialized thread designs, our team is ready to assist. Contact us today at info@joyeequipment.com to discuss your requirements and unlock reliable oilfield solutions.