This Plantronics A10-12 Direct-Connect headset cable is for call centers which are using both Plantronics Polaris brand headsets and amplified headset solutions like the M12 or M22 Vista combined with any H-series headset (e.g. HW251).
The A10 adapter cable enables for Plantronics standard H-Series headsets (e.g HW251 SupraPlus) to be connected to direct-connect telephones (equipped with A10 compatible RJ9 (smaller version of RJ11 modular jack port).
This is the Plantronics A10-12 Cable is the same cable as the regular Plantronics A10 Cable, except it has 4dB higher output. In case you have a direct connect office phone (i.e. Nortel) and need higher volume, you can use this cable instead.
Use this cable only in case your direct connect headset volume is too low. It may cause distortion in case your phone already has high output volume.