I found this in an Attic today.
Was installed on 14 Romex Wire In-Line.
I could not trace the circuit as the cable left a Junction at the Gable End Wall and passed down thru a top plate of a wall below.
I think it is some type of inline Fused Link but not sure.
Markings on one side are printed UL and the word AMP
On the Other side is imprinted 300 volt 20 amp
and use 14 wire only…
My concern is that on the one side are 3 Exposed Connectors.