This is the body for a 3-band, base loaded ham radio antenna for 40, 30, and 20m.
It is designed to be used with a 6m fiberglass mast from lambdahalbe.de; it may fit other similar masts.
You need 2mm gold-plated plugs (normally used for RC car batteries etc.) ad 0,6 - 0.7 mm enamel wire for the loading coil. The radiator should be made ca. 5 m long so that the coil sits ca 1m above ground.
The coil should be ca 1 - 2 turns for 20m, 6 - 7 more for 30m, and 8 more for 40m, but you need to tune this to resonance..
Use 2mm plugs to shorten the parts of the coil not needed for the band in use.
More details are here: http://reflector.sota.org.uk/t/sota-vertical-antenna-for-40-30-20m/15673.
You can fit in a small balun behind the BNC plug; use 11 turns of twisted enamel wire on a FT50-43 toroid then.
73 de Martin, DK3IT
Edit 2018-03-15: As a compact winder for winding up the tuned radials, I recommend the design from https://www.thingiverse.com/thing:1173824/ but scaled to 66% in the X and Y axis and 100% for the Z axis (3 mm high).