A mass coupler was a part used in podracers. It was also useful as a trade item.
Anakin Skywalker needed a mass coupler to fix his podracer before the Boonta Eve Classic. Qui-Gon Jinn was able to obtain one by either trading an engine binder and a hydrospanner to Mawhonic, two fuel converters to the Important Merchant, or a Naboo Fusion Coil and an engine binder to the Important Merchant.
Qui-Gon could also obtain the mass coupler by killing the Important Merchant or Mawhonic and stealing it from them, but Anakin would then refuse to accept it.
Anakin Skywalker needed a mass coupler to fix his podracer before the Boonta Eve Classic. Qui-Gon Jinn was able to obtain one by either trading an engine binder and a hydrospanner to Mawhonic, two fuel converters to the Important Merchant, or a Naboo Fusion Coil and an engine binder to the Important Merchant.
Qui-Gon could also obtain the mass coupler by killing the Important Merchant or Mawhonic and stealing it from them, but Anakin would then refuse to accept it.