They conclude that it is the inboard one third of the large right wing flap adjacent to the flaperon recovered from La Réunion Island last July.
The paper is likely to increase the focus on possible reasons why most of the debris recovered from the Malaysia Airlines 777-200ER has been identified as coming from the right side of the jet.
MH370 vanished over the Gulf of Thailand while flying from Kuala Lumpur to Beijing with 239 people on board on March 8, 2014.
The ATSB analysis of the last signals sent from an onboard server on the jet via an Inmarsat satellite and a ground station says it is possible that they were interrupted by the out of fuel jet losing line of sight with the satellite as the fuselage rolled over or inverted immediately before impact with the south Indian Ocean.
MH370 smashed into the sea with enough force to create the mostly small fragments of floating wreckage recovered until now, including stripping or breaking some internal fittings from their settings.
Fresh questions about the possible location of the sunk wreckage of the Boeing 777 have been raised by some of the Independent Group of scientists. These add to pressure on the ATSB managed seafloor search to also look at an area well to the north-east of the current and nearly exhausted priority zone.
This likely largest part of MH370 yet recovered was found on the eastern side of the Tanzanian Island of Kojana, which is a more precise location than the term Pemba island previously applied to the discovery.
As the authors of this latest report explain, a bolt head seen in the photos posted of the wreckage carries the relevant part number for its use in this section of Boeing 777-200s and -300s.