The MFJ-16C06 is a six-pack of dog bone ceramic glazed centre or end insulators.
It will not break with long antennas and will not arc over or melt even under full legal power. Moulded ridges give an extra long path to prevent high voltage breakdown. Smooth wire holes prevent wire damage.
The 16C06s can be used as a centre or end insulators for diples, doublets, G5VRs, guy wire, or vees.