Key points for selecting PG thread specifications

Match according to the size of the connection object
Outer diameter matching: If the connection is a component with an inner diameter of about 15mm, PG9 (outer diameter 15.2mm) may be more suitable from the perspective of PG thread specifications. Make sure that the outer diameter of the PG thread matches the hole diameter or shaft diameter of the connection component. It should not be too large to cause assembly failure, nor too small to cause loose connection or excessive gap. For example, in the connection of electrical equipment, if a cable protection tube is connected to the interface of the equipment, and the inner diameter of the cable protection tube is 12mm, then it is more appropriate to choose a PG7 (outer diameter 12.5mm) thread specification, which can ensure that the threaded part can smoothly cooperate with the equipment interface during installation and provide sufficient connection strength.
Pitch adaptation: The pitch determines the density of the thread. The choice of pitch is particularly important when the connection length or connection force transmission needs to be precisely adjusted. For example, in the assembly of some precision instruments, if the position of a component needs to be fine-tuned, choosing a PG thread with a suitable pitch can more accurately control the adjustment range. For example, the pitch of PG21 is 1.588mm, which may be selected in some equipment assembly that requires a relatively large pitch to quickly achieve connection but has certain requirements for accuracy; while the pitch of PG7 is 1.270mm, which may be more suitable in some occasions that require higher connection accuracy and more precise adjustment.

Consider the tightness requirements of the connection
Sealing requirements: If the application scenario is the connection part in the liquid or gas transportation pipeline system, and leakage needs to be prevented, it is necessary to select a PG thread specification that can provide better sealing performance. For this case, in addition to the specifications of the thread itself, sealing elements such as sealing gaskets may also be required. For example, in a chemical pipeline system, when conveying corrosive liquids, it is necessary not only to select a PG thread with a suitable outer diameter and pitch, but also to ensure that the threaded connection can be tightly sealed to prevent liquid leakage from causing safety hazards and environmental pollution.

Tightening force requirements: Different equipment or structures have different requirements for the tightening force of threaded connections. In some cases that are subject to large vibrations or loads, such as the connection of automobile engine parts, it is necessary to select a PG thread specification that can provide sufficient tightening force. This may involve selecting a thread with a larger outer diameter or a suitable pitch to ensure that the connection will not loosen under long-term vibration and load.

Based on working environment factors
Temperature influence: In a high temperature environment, the material will expand thermally and the size of the thread will change accordingly. If PG threads are used in a high temperature environment (such as equipment connection near an industrial furnace), consider selecting specifications that can adapt to this thermal expansion change. For example, the impact of relative size changes of larger PG thread specifications when the temperature changes may be smaller than that of smaller specifications, and the strength and stability at high temperatures should also be considered in the selection of materials.

Corrosive environment: If there are corrosive substances in the working environment (such as equipment in a marine environment, chemical production workshops, etc.), it is necessary to select PG thread parts made of corrosion-resistant materials, and the specification selection should also consider the thread form that can facilitate anti-corrosion treatment (such as coating with anti-corrosion coating, etc.). For example, when selecting PG thread specifications for electrical equipment connections in a marine environment, it is necessary to give priority to stainless steel thread parts, and select the appropriate outer diameter and pitch to ensure that they will not be corroded for a long time in the marine salt spray environment to ensure the reliability of equipment connection.