Hello, i have a strange surplus (???) object to understand...

It is a metallic container, sealed, with a "BNC" female on the left and a
"N" female on the right.

Size is 11,5 x 5 x 7,5 centimeters.

On the top i can read this :

FCC-550-230-75-NB1
FSCM: 53779
DATE CODE: 8912
S/N 337

A photo here :

http://www.arifidenza.it/Public/data...38_piccola.jpg

It should be a sourge arrestor, but i need the exact specifications.
Can this be useful for an amateur radio station or it is completely useless?

Thank you,,
73 de Riccardo IK5WQO