Inner flat type: Mainly used for outer thickening of Drill Rods. Its characteristic is that the Drill Rods has the same internal diameter and low drilling fluid flow resistance; but the outer diameter is large and it is easy to wear.　Cross-eye type: Mainly used for thickening Drill Rods inside and outside. Its characteristic is that the Drill Rods has two inner diameters, the flow resistance of drilling fluid is greater than the inner flat type, but its outer diameter is smaller than the normal type. Formal style: Mainly used for inner thickened drill pipes, drill bits, and fishing tools. Its characteristic is that the inner diameter of the thickened joint is smaller than the inner diameter of the pipe, and the flow resistance of the drilling fluid is large. Among the three types of buckle, the relative flow resistance is the largest, but the outer diameter is the smallest and the strength is greater. The above three types of joints all use V-shaped threads, but the buckle type, buckle distance, taper and size are very different.

The digital series connector is the American National Standard Coarse Thread Series. It has been adopted as an international standard by API. NC threads are also V-threads. Some NC-type connectors have the same pitch diameter, taper, pitch and thread length as the old API standard connectors, and can be used interchangeably.

Petroleum Drill Rods joints mostly adopt the form of outer thickening or inner and outer thickening. The outer diameter of the Drill Rods joint is larger than the outer diameter of the pipe body. During the drilling process, it constantly contacts and frictions with the well wall or casing, resulting in abrasion. In order to avoid joint wear and break drilling For drilling accidents such as rods, tripping, etc., Drill Rods joint wear-resistant belts must be installed on the Drill Rods female joints.