SAE

SAE threads, the thread standard developed by the Society of Automotive Engineers (SAE), are widely used in automotive, aerospace, machinery manufacturing, and other fields.
The SAE thread standard includes a variety of types, the more common of which are SAE Straight Thread and SAE Tapered Pipe Thread (e.g., NPT/NPTF).

SAE Straight Thread

SAE Straight Threads, also known as SAE Standard Straight Threads or UN/UNF Threads, are very common in North America. The designation is usually “OD-Pitch UN/UNF”, e.g. “3/4-16 UNF”. These threads often follow the SAE J1926 standard when connecting to a hydraulic system, where a countersunk hole is machined in the port and an O-ring is used to seal the thread, while the thread itself primarily provides the tightening force.

SAE Tapered Pipe Threads

SAE tapered pipe threads mainly include NPT (American Standard Tapered Pipe Thread) and NPTF (American Dry Seal Tapered Pipe Thread).

NPT threads: the top of the tooth is not a sharp point, so there may be a small leakage point after assembly, usually requiring the use of sealant to seal.
NPTF thread: similar to NPT thread, but its sealing performance is better because the sealing relies on the occlusion between the top and bottom of the threaded teeth, and usually does not require additional sealant. However, where conditions permit, the use of a sealant can further increase the reliability of the seal.

SAE Thread Specifications and Sizes

SAE threads are available in a wide variety of sizes and dimensions, covering a wide range of sizes from tiny to larger. For example, SAE straight threads can range in size from 5/16-24 to 3-12, and tapered pipe threads can be made in a variety of nominal sizes from 1/16 to 4 inches.

SAE Thread Application Areas

Because of their excellent sealing and fastening properties, SAE threads are used in a wide variety of applications where connections and seals are required, such as automotive engines, hydraulic systems, aerospace equipment, and oil and gas pipelines.

Metric Thread

Also known as metric thread, it is a standardized thread specification that is widely used in internationally accepted dimensional specifications. The following is a detailed analysis of metric thread:

Metric Thread Definition and Characteristics

Definition: Metric thread is a thread labeled in millimeters, and its tooth angle, pitch, internal and external thread fit and other aspects are standardized according to the international metric standard.

Characteristics: Metric threads are characterized by high degree of standardization, good interchangeability and wide range of applications. Its size marking is clear and explicit, which is convenient for international communication and cooperation.

Metric thread classification and marking

Classification: Metric threads can be divided into many types according to different tooth angles, such as the common 60° metric ordinary thread (M) and so on. In addition, there are metric small threads (mainly used in watch and instrument industry), metric aerospace threads (mainly used in aircraft, spacecraft products) and so on.

Marking: The marking of metric threads usually starts with the letter “M”, followed by the nominal diameter × pitch (for fine threads also need to mark the pitch) form of expression. For example, M10×1.5 indicates that the nominal diameter is 10mm and the pitch is 1.5mm.

Metric Thread Application Areas

Because of its high degree of standardization and good interchangeability, metric thread is widely used in the connection and fastening of various machines, equipments and instruments. Especially in international trade and transnational cooperation, the application of metric thread is more common.

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