The tool used to cut inner threads can be seen here. It needs to be
very sharp for proper finish quality in plastic.
This is how the completed base looks, when mounted on the car roof. Sorry, I did not wash the car before installing the antenna!
Note how the O-ring extends slightly above the surface of the base plate.
When the antenna is dismounted, a simple cap is screwed onto the base, in order to protect the contacts from dirt, water and corrosion. This is how the car roof looks with dismounted antenna. Only the quarter wave whip for VHF remains in place at all times, since it fits easily into most garages. The other wires in this photo are power and phone lines in the background!
A threaded insert, larger than that of the base but otherwise similar, is screwed into the cup. It takes an M3 bolt that serves a double purpose: It holds a solder lug providing ground connection to the antenna innards, while also locking the threaded insert in place, so it won't unscrew from the cup when installing or removing the antenna from its base.
Note that the four holes used for the bolts that hold the servo mounting plates are NOT in a square arrangement, but a rectangular one. These holes can be drilled using a drill stand, or using the lathe configured as milling machine. They must be drilled in the proper locations, so that later the contact spring for the coil end properly rests on the coil contact plate.
Likewise, the threaded hole in the brass insert must be drilled in the
proper location, so that the solder lug will be roughly centered under
the end of the servo, when the insert is correctly screwed into the cup.