What do you think this is/was?

sushi roll

vacuum cap

antenna feed horn

choke ring antenna


Answer: Vacuum cap



The people who answered it right were:

dl9kr
G4AXX
Ann Oying
KX0R
WQ8C
K9HA
K8YK
K7CW
PA0OLD Jaap
W4GSM
OH3PC
is0vsg
DK8VS
iv3guy
Ghost of Fessenden
kc0mjp
WP3EX
HP1DJJ
N8OKR
W2DTC
No Code Xtra
pa5cw
WØRI

Thanks to everyone who gave it a try.