UHF coaxial connectors and adapters are general-purpose devices developed for low-frequency systems from 0.6 - 300 MHz. Originally intended as a video connector for radar equipment, it is by far the most popular type in amateur radio
The UHF connector was designed in the 1930s by a designer at Amphenol for use as an RF connector in the radio industry.
UHF males are referred to as "PL-259" and females as "SO-239".
Characterized by its threaded connection, the UHF connector is widely used because of its ease of assembly. The UHF solderable screw-type termination feature does not require special crimping tools.
These connectors have a threaded connector, which prevents them from being accidentally removed. It allows them to be tightened enough to make a good low-resistance connection between the two halves.
The UHF connector thread is 5/8 inch 24tpi UNEF standard. It's worth noting that the center conductor jack on the SO-239 can also accept banana plugs. This is useful for some test applications that require access.
PL259 connectors are available in two sizes: thick coax and thin coax. Typically, larger-sized versions are used with RG-8/U or RG-9/U, while smaller versions are better suited for cables including RG-58/U. The basic connector remains the same, but the cable entry area is modified for the associated coax.
Thin cables are typically used for short or "chip" leads, but not for long wires because thinner cables have higher losses than thicker cables. When a thin cable variety is required, the PL259 plug is often used with a "reducer" to fit the large cable entry hole in the plug to the thin cable. Interestingly, the term "PL259" originally referred to a specific mechanical design, although it is now a more general term referring to UHF male connectors.
UHF Specifications