Fixed bulkhead  type attenuators (Adapter type) utilizes the air gap between two connectors to achieve the optical attenuation. This fixed optical attenuator has a similar structure of a standard female-female fiber adapter. It is simple, low-cost and compact.

They are recommended for use where return loss is not a concern nor is absolute attenuation value. The attenuators are available in ST/PC, FC/PC, or SC/PC format, with fixed attenuation values of 3dB, 5dB, 10dB, 15dB, and 20dB. Multimode or Singlemode fiber optic attenuators can be supplied for operation at 850nm, 1300nm, or 1550nm.