The standard sensor has a cylindrical spigot which fits into a vertical hole
in the cross arm,
and is secured with a screw (horizontal) in the cross arm.
The sensor spigot is 10mm diameter, and projects 40mm below the body of the sensor.
The sensors can alternatively be made with a BSP 0.5" (say) screw thread,
to screw into the top of a water pipe mast (also threaded),
or with a threaded bolt hole in the bottom, with mating bolt.
Price is the same for all.
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