I agree with Bob as it NOT being factory.
Some 1960's inline fuse holders look like that. If this is indeed a fuse holder, look for a seam running linear to the length. If a fuse holder, you'll likely find a couple release tabs that open the outer clam shell. Inside, you would find a fuse.
Seeing that the speaker lead is also spliced, a repair person may have used this as a means to repair original cut wires, as opposed to going inside the chassis to solder in a connection...an easier, softer way.