For any Italeri/Revell/Meng/Takom Leopard 1
Turned aluminium barrel - with rifling - plus 8-part resin sleeve, fume extractor and optional collimator/counterweight
The sleeve is broken into separate elements to give you more flexibility. This sleeve was used by the Australians (AS1) and Canadians (C1 and C2). The clips are much simpler than the more familiar 'German' version. The collimator was only used on the Canadian C2.
The flat at the end of the barrel is on the left (looking forwards). Part 1 has a joint along its length. There was no fixed position for this so check references for the vehicle you are building.
Part 3 has a weld which should be positioned along the bottom.
Part 4 has locking catches. The square part of the catch goes on top on the left side (looking forward).
Parts 5 and 6 have straps which go underneath the barrel. In reality, there is a spacer piece which is impossible to cast. Therefore, cut a rectangle of paper (perhaps sticky label) 4.5 mm wide to position between the two parts. Fit across the top of the gap and trim the depth to match the joint along the thermal sleeves.
A review can be found here (MSC Review Connect), here (MilitaryModelling.info) and here (Armorama).