What are these things?

Standoff insulators

Mineral blocks for cattle

Ceramic resonators

High voltage capacitors

Answer: Ceramic resonators. Electrically, these often take the form of a shorted quarter wave transmission line. Due to the really high dielectric constant of the ceramic, they can be made much smaller than the equivalent air or plastic insulated line. For example, a 400MHz resonator can be made about 0.5 inch long , instead of the 5 or 6 inches it would take with coax.