For any Italeri/Revell/Meng/Takom Leopard 1
Resin barrel - with rifling - plus resin counterweight and fume extractor
This is the basic 105 mm L7 gun used on all early production Leopard 1s - and indeed on many other types of tank such as Centurion, M60, etc.
The flat at the end of the barrel is on the left (looking forwards).
Part 1 has a weld which should be positioned along the bottom.
The fume extractor should be positioned 30.5 mm from the base of the barrel ~ see above.