The caphat is from DX Engineering. It's threaded on to a rigid mast similar to a Wilson or Hustler mast with 3/8 x 24 threads. It's just a hub with holes drilled out for the rods.Thank you for the photo of your HF Screwdriver Antenna with Cap Hat added.
Your Cap Hat appears quite similar to the 6 element grounding add-on base I showed above, but instead of wedging between the coax and antenna coil, yours is somehow mounted on top. For the grounding star, it has a PL259 pass through, connecting the elements only the the outer shield, electrically. But if used as a cap hat, for THAT item, it would expose the SO239 (underside) pointing straight up, collecting rain.
Where did you buy your cap hat, or was it fabricated using a modified grounding base?
They sell a smooth bore hub designed to slip over the Hustler antenna but unless you modify the loading coil if used on a CB resonator, it won't tune up on that band but instead probably tune up on a lower band like 15 meters. That's exactly the purpose of a caphat, to decrease loading coil inductive losses with mobile antennas shorter than a 1/4 wavelength. With a non adjustable coil, the caphat will tune up on a band or 2 lower than orginal antenna design (assuming starting with a CB antenna) depending on the caphat size. Think of it like adding extra feet to the antenna height.
You can easily make your own coil with enameled wire and some PVC parts and antenna hardware to use a capacity hat on. I've done this myself and it works well even though it isn't as pretty like the mass produced antennas.
If you can find a used Hustler 6 meter mobile antenna (RM-6), it'll work perfect with a caphat on the CB band. These are no longer made but still show up on Ebay.
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