From Bartolini:
The M34C-T is an M3 Soapbar shaped bass pickup for the bridge position. It is 3.50″ / 88.90mm long and 1.50″ / 38.10mm wide. The dual coil design features deep tone.
The “original series” bass pickups with passive designs. They are cast in epoxy to remove unwanted feedback and microphonics.