Richard, i believe that, these manilhas are not
directly associated with the slavery phenomenon but, only circumstancially. Indeed their basic purpose was that of exchanging currency units, as also other implements of similar kind, where their metal (bronze) contents represent their intrinsic value, in cultures where money was (is) not based in coins and notes, valued by Central bank treasures (so they say
).
I have once bought a rather nice example, which i offered to my daughter. Although they may be considered, judging by their shape, as actual bracelets, the one of mine, for one, although rather sturdy, was to narrow to fit my young daughters wrist, meaning that their purpose was (only) directed to market currency, that not for adornment.
Other members will most probably contest my assessment
.