Here are some common applications that use (British Standard Pipe) BSP thread fittings:
Plumbing systems
BSP is commonly used for water pipes, gas pipes, sanitary fittings in commercial and residential plumbing systems in the UK, Europe and some other regions.
Compressed air lines
BSP fittings are often used to connect pneumatic components and build compressed air distribution piping networks.
Industrial process systems
Things like chemical transfer lines, oil/lubrication systems, hydraulics frequently use BSP fittings for their durability and pressure handling.
Instrumentation
BSP allows connection of pressure gauges, sensors, valves to sample ports or process pipelines in industrial facilities.
Heating/cooling systems
Distribution of steam, hot/chilled water etc. within heating units, boilers, chillers etc. uses BSP fittings extensively.
Welding/gas equipment
BSP thread gas cylinder valves connect to manifold distribution pipes and torch connections.
Oil & gas production
Found in piping for extraction, refining, storage of petroleum and natural gas.
Marine applications
Used onboard ships for seawater intake/discharge lines, firefighting systems and engine/generator cooling.
The metric sized BSP thread is durable and makes for reliable leak-free joints under pressure, vibration and temperature cycling.