In the oil and gas industry, STC and LTC refer to specific types of thread connections used on API (American Petroleum Institute) casing. Both are variations of the API Round Thread (which has 8 threads per inch), but they differ in length and performance capabilities.
Unsure whether LTC or STC threads fit your well? Fill out our form, and our engineers will analyze your project specs to recommend the optimal thread type-free of charge.
STC (Short Thread Coupled)
Definition: As the name suggests, the threaded section on the pipe and the coupling is shorter than that of the LTC.
Design: It features a 8-round thread profile (8 threads per inch).
Strength: Because the thread is shorter, it has a lower tensile strength (the amount of pull it can withstand before the threads "pull out" or jump).
Applications:
Used in shallower wells where the weight of the casing string is not extreme.
Used in applications where high tension is not a primary concern.
Generally the most economical option.
LTC (Long Thread Coupled)
Definition: The threaded section is longer than STC, providing more "thread engagement."
Design: Like STC, it uses an 8-round thread profile. Visually, they look identical except for the length of the threaded area.
Strength: The additional length means more threads are engaged between the pipe and the coupling. This provides significantly better resistance to axial tension (pulling force) and improved leak resistance compared to STC.
Applications:
Used in deeper wells where the casing string is very heavy.
Used in environments with higher longitudinal loads.
Currently the most common thread type for standard casing strings.
Key Comparison Table
| Feature | STC (Short Thread) | LTC (Long Thread) |
| Thread Length | Shorter | Longer |
| Thread Profile | 8-Round (API) | 8-Round (API) |
| Tensile Strength | Lower | Higher |
| Leak Resistance | Good (standard) | Better (due to more engagement) |
| Common Use | Surface casing, shallow wells | Production casing, deep wells |
| Cost | Less expensive | Slightly more expensive |
Thread test equipments
API 5CT Thread Factory
API Threads certificate
FAQ
What is the API standard for threads?
API thread standards are primarily established by the American Petroleum Institute (API); the core specifications-API SPEC 5B and API SPEC 5CT-serve to standardize the design and inspection of threaded connections for oil casing, tubing, and drill tools.
API SPEC 5B: Defines thread geometric parameters, gauge inspection methods, and tolerance requirements. It covers various thread types-including short round threads (STC) and buttress threads (BTC)-thereby ensuring interchangeability among products from different manufacturers.
API SPEC 5CT: Specifies the material properties, mechanical strength, and service conditions for casing and tubing. It references the thread forms defined in the 5B standard, explicitly delineating their applicability across different steel grades and operating environments.
What are the different types of treads?
The primary types of API threads include Short Round Thread (STC), Long Round Thread (LTC), and Buttress Thread (BTC), each suited to different well conditions.
STC (Short Thread Connector): Short Round Thread features a relatively short thread length. Its connection strength typically ranges from 60% to 80% of that of the pipe body. It is predominantly used in shallow wells or low-pressure environments, offering the advantages of simple manufacturing and low cost.
LTC (Long Thread Connector): Long Round Thread features a greater engagement length, providing enhanced sealing performance and load-bearing capacity. It is suitable for medium-to-deep wells and operating conditions involving higher pressures.
BTC (Buttress Thread Connector): Buttress Thread features a superior load-bearing flank design, enabling it to withstand greater axial tensile forces while maintaining excellent gas tightness. It is widely utilized in demanding environments-such as deep wells and high-temperature, high-pressure conditions-and serves as the foundational prototype for many specialized thread designs.
