[Andrew2]

The threaded section and the silver pipe are usually two separate items, which I believe is what you have ... the pipe has a slightly smaller diameter - it is fitting inside the threaded section ... the brown (rusty) tape has been used to provide an external jointing seal in the absence of the correct fittings

If you are concerned about a leak then source a plumber to correct it ... but given that there is negligible water pressure on the joint it should be OK ... maybe source some fresh Oakum / Denso tape to reseal if it does start to leak