For sale are these (I believer they all are NOS new) tube amp 10 amp 120 - 250V AC interference filters 

you run the 120V hot power through them, with the grounded section to a grounded chasis.  Price is $1 each

They are about 1x2x2".  Last one to see is a little thicker 15 amp version.  They have a little sawdust on them.