In the context of finance and investing, LTC and STC usually stand for Long-Term Capital Gains and Short-Term Capital Gains.
These terms refer to the profit you make when you sell an asset (like stocks, bonds, real estate, or cryptocurrency) for more than you paid for it. The distinction between the two is based on the holding period-how long you owned the asset before selling it.
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STC (Short Threaded and Coupled)
STC refers to a Short Round Thread connection.
Design: It features a shorter threaded section at the end of the pipe.
Strength: Because the threaded engagement is shorter, it has lower tensile strength (resistance to pulling apart) compared to LTC.
Best For: Shallow wells, surface casing, or environments where the weight of the pipe string is not extreme and high internal pressures are not a primary concern.
Advantage: It is generally more economical and faster to make up (connect) on the rig floor.
STC threads Specification
| Parameter | Specification / Value | Remarks |
| Thread Form | Round Thread | Both crests and roots are rounded |
| Threads Per Inch (TPI) | 8 TPI | Common API standard |
| Thread Pitch | 3.175 mm (0.125 in) | Axial distance between adjacent threads |
| Taper | 1:16 (6.25%) | Ratio of diameter change relative to length |
| Included Angle | 60° | The angle between the thread flanks |
| Thread Height ( hn ) | 1.810 mm (0.07125 in) | Vertical distance from crest to root |
| Crest Radius ( rn ) | 0.432 mm (0.017 in) | Reduces stress concentration |
| Root Radius ( rrn) | 0.508 mm (0.020 in) | Enhances structural strength |
| Effective Length ( L4) | Short | Varies by pipe OD (significantly shorter than LTC) |
LTC (Long Threaded and Coupled)
LTC refers to a Long Round Thread connection.
Design: It has a significantly longer threaded section ( L4 length) than STC.
Strength: The additional threads provide more surface area for engagement between the pipe and the coupling. This results in higher tensile strength and better leak resistance under tension.
Best For: Deep wells, heavy casing strings, and high-pressure environments where the pipe must support its own massive weight hanging in the hole.
Advantage: Provides a more secure, robust connection for demanding downhole conditions.
LTC Threads Specification
| Parameter | Specification / Value | Remarks |
| Thread Form | Round Thread | Both crests and roots are rounded |
| Threads Per Inch (TPI) | 8 TPI | Same as STC |
| Thread Pitch | 3.175 mm (0.125 in) | Axial distance between adjacent threads |
| Taper | 1:16 (6.25%) | Diameter change of 0.0625 inches per inch along the axis |
| Included Angle | 60° | The angle between the thread flanks |
| Thread Height ( hn ) | 1.810 mm (0.07125 in) | Vertical distance from crest to root |
| Crest Radius ( rn ) | 0.432 mm (0.017 in) | Reduces stress concentration |
| Root Radius ( rrn ) | 0.508 mm (0.020 in) | Increases root strength |
| Effective Length ( L4 ) | Long | Core feature; 25% to 50% longer than STC |
Differences
| Feature | STC (Short Thread) | LTC (Long Thread) |
| Thread Length ( L4 ) | Shorter | Longer (typically 25-50% more) |
| Connection Strength | Moderate | High |
| Well Depth | Shallow to Medium | Deep Wells |
| Seal Integrity | Good | Better (due to more thread engagement) |
| Steel Grades | Usually J55, K55 | Usually N80, L80, P110 |
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FAQ
What is the difference between STC and LTC threads?
STC (Short Round Thread) and LTC (Long Round Thread) are common connection types for oil casing. The main difference lies in thread length: STC has shorter threads, offering lower strength, suitable for shallow wells or low-stress environments; while LTC features longer threads, providing tighter engagement, higher tensile strength, and better sealing, making it ideal for deep wells or heavy-duty applications. Despite the difference in length, both share the same thread profile and threads per inch.
What are the three types of threads?
API standards primarily define three thread types for casing and tubing: STC, LTC, and BTC. STC (Short Round Thread) is used for shallow wells where tension is low. LTC (Long Round Thread) features a longer threaded section for better strength in deeper wells. Unlike the round profiles of STC and LTC, BTC (Buttress Thread) uses a trapezoidal shape designed to handle maximum axial tension and heavy loads in the most demanding deep-well environments.
