Round Thread

Definition - What does Round Thread mean?

A Round Thread is a profile made on the tools and components used for slickline operations in a wellbore. It is also known as a knuckle thread. This Thread is robust and can cause minimal wear and tear by dirt and other impurities inside the wellbore because of their round shape. The Round Thread profile is prepared as per API tubing grades.

Petropedia explains Round Thread

The strength of round thread can be calculated by the following equation:

Pj = Min (Pj1, Pj2)

Where, Pj1 refers to fracture strength and Pj2 refers to pullout strength of the connection.

Fracture strength (Pj1) can be calculated as:

Pj1 = 0.95 x Ajp x Up


Ajp = Circumference area of a pipe wall in square inches.

Up = Minimum ultimate strength of pipe in psi.

Pullout strength (Pj2) can be calculated as:

Pj2 = 0.95 x Ajp x L x [(0.74D-0.59 Up)/(0.5L + 0.14D) + Yp/(L+0.14D)]


Yp = Minimum yield strength of pipe in psi.

D = Nominal outside diameter of pipe in inches.

d = Nominal internal diameter of pipe in inches.

L = Length of engaged thread in inches.
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