The coils shown in the pictures below are all modern voltage driven types. The single output coil has a large metal clamp so it can be bolted to the the metal framework of the vehicle. The twin output coils have two studs which need to be bolted to a metal heatsink source such as the framework of the motorbike. This can be seen in the pictures featured in page ' Redundant spark ignition'. The twin output coil is mounted underneath the seat and is fixed by the studs to the metal of the battery box.
A modern six volt single ended ignition coil.
6 volt and 12 volt double ended coils
Ignition circuit with single ended coil and distributor.
Ignition circuit showing twin output coil