1. Commonly Used Tubing Thread Type
Thread types frequently used for the tubing can be divided into EU, NU, and New VAM. All these three types can be found in tool shops. It is difficult to distinguish EU from NU in terms of the thread appearance, because both of them are triangular shaped. However, we can find their difference in accordance with the entire tubular pile. EU means external upset, while NU refers to non upset. Actually, New VAM is a kind of trapezoidal thread and its cross section has a rectangular shape. Also, this type is not external upset. Thus, it can be easily distinguished. Next, we will introduce these three thread types in detail.

EU, also called External upset
EU is a type of external upset tubing thread. On the shop shelves, three types of mark concerned with EU can be found. Among them, EUE means external upset end. EUP refers to external upset pin, and EUB is external upset box. In addition, the word pin can be replaced by other words, such as external thread, male, or male thread. Also, we can use such words as female thread, internal thread, or box thread instead of the word box.

NU, also called Non upset
NU represents the non upset type tubing joint. Another difference between NU and EU is that NU usually has 10 teeth per inch and EU often owns 8 teeth per inch. Moreover, NUE refers to non upset end, or end non upset. Similarly, E means the word end. The above statement comes from the Petroleum Dictionary.

New VAM
This type thread type is prominently characterized by its basically rectangular section, equal intervals of pitch, as well as the non external upset design. It can be always found in the production of sliding sleeve ends in workshops.

2. Drill Rod Thread Type in Common Use
The commonest drill rod thread types are RFG and IF. Other types like FH can not be found in tool shops. In accordance with the rich experience of a master worker, REG and IF thread types respectively possess 5 teeth per inch and 4 teeth per inch. In some cases, REG thread also has 4 teeth per inch if its outer diameter is more than 4-1/2". In other words, REG thread always has the outer diameter of over 4-1/2" and most IF thread possesses the outer diameter of less than 4-1/2".

REG, API Regular Thread
This type thread is adopted by the regular drill rod joint. It has ever been used to connect the internal upset drill pipe, which forms the drill rod joint with its inner diameter smaller than that of the drill rod upset end. Furthermore, the inner diameter of the drill pipe upset end is smaller than that of the drill pipe body.

If we touch both REG and IF types thread, we will feel different. The REG thread is fine and smooth, but the IF thread is a little rougher. It is because their distinct densities of thread per unit length.

IF, API Internal Flush
The internal flush type drill rod joint utilizes the IF thread. This type thread serves to connect the external upset type, or the external and internal upset type drill pipe, so as to make the inner diameter of drill pipe joint equal or close to that of the drill pipe upset end or the drill pipe body.

FH, API Full Hole
Just as its name implies, the full hole means that the hole is as large as the eye. The eye refers to the inner diameter of both drill pipe joint and drill pipe upset end. Their inner diameter is smaller than that of the drill pipe body.

3. Commonly Used Thread Type of Blind Drainage Pipe and Sieve Tube
LTC, Long Thread Connector

The LTC type has the same thread shape as the STC type, so these two types can be connected. However, the connection is actually not allowed, because the maximum torque values they can bear are different.

STC, Stub or Short Thread Connector
Both STC and LTC types thread belong to the API standard thread. Their difference only lies in the thread length. The LTC type is longer than the STC type. Under the same condition of 4-1/2" long outer diameter pipe, the LTC type usually possesses the thread length of over 3 inches, while the STC has less than 3 inches of thread length.

BTC, Buttress Thread Coupling
BTC can be easily distinguished from LTC and STC, but it looks much like the New VAM type. The distinction can be made between BTC and New VAM only from the usage or the outer diameter of the tubular pile.

4. Wash Pipe Thread Type in Common Use
A wash pipe is often applicable to sand control completion. It mostly acts as the passageway for the filling liquid. Thus, the tubular pipe primarily has no coupling and non upset design. Only 1.9 inches long wash pipe is the external upset type, because its wall is too thin. If the thread is made without the external upset design, the mechanical properties of the whole tubular pile will be badly influenced.

The wash pipe thread often found in the workshops can be classified as three types, including Hydrill 511, Hydrill CS, and TSWP. Hydrill 511 usually has the diameter of 2-7/8", and Hydrill CS typically possesses the diameter of 1.9". Others like 4" belong to the TSWP type. Among them, both Hydrill CS and TSWP are buttress thread. They look the same, which can only be separated in accordance with their outer diameter.

TSWP, Baker Oil Tools Wash Pipe
TSS, Baker Oil Tools Special
Hydrill 511
5. Frequently Used Sealing Stub Thread
ACME Thread

The sealing stub thread mostly is ACME type. This type thread is prominently characterized by its trapezoidal or approximately rectangular cross section. In front of the pin thread, there is usually an elongation segment without thread.

6. Other Thread Types
FL-4S Thread

FL-4S thread can be found in the pressure test plug. This type thread has an approximately right angled trapezoidal cross section.

LP Thread
LP thread can be seen in the thread-changing joint. The thread is usually short and the thread angle is small. The diameter of the root of pin thread is the same as that of the cylinder.

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