Some implementations of the disclosure relate to an adapter, comprising: a channel running through the length of the adapter from a first opening to a second opening of the adapter, wherein a shaft of an endoscope is configured to be threaded through the channel; a first coupler configured to removably secure the adapter to a second coupler of the endoscope, the first coupler comprising the second opening; and a rigid attachment segment comprising a surface configured to removably couple the adapter to an instrument or second adapter. The surface of the rigid attachment segment may include multiple grooves and sections alternating along the longitudinal length of the rigid attachment segment, each section protruding relative to the grooves and comprising a recessed indentation or protrusion; and the multiple sections and grooves configured such that the instrument or second adapter can be coupled to the adapter in multiple lengthwise positions.