Both aluminium and carbon models can be made using a monocoque method.
This simply means that all the tubes are made in one ‘mono’ piece.
A continuous tube means less moving parts in connection with the boom head.
If booms arms are glued or screwed onto the boom head there are multiple materials coming together with different material properties that increase the chances of failure over time.
Forming the shape of the arms in one single section equals less joining points for stress to focus on and fewer components such as screws, glues etc. to potentially fail, which significantly increases the structure’s lifespan. (And in carbon booms with separate arms, which cannot reliably be joined by rivets or screws like aluminium models, that means only glue’s holding the whole structure together!)
Instead, one rigid, constant shell means a boom tube can pass through a clamp or boom head with less risk of failure at that point and delivers greater levels of stiffness too.
Monocoque: LESS = MORE!