One end of this 2" diameter x 3.5" long extension tube fits into 2" focuser drawtubes. The opposite end is a 2" diameter eyepiece holder that uses a non-marring brass clamp ring to hold 2” eyepieces and accessories in place. The captive thumbscrew that tightens the clamp ring can’t be lost in the field. This extension tube makes up for the loss of light path photographically when a 2" star diagonal is removed from many scopes and replaced by a camera and camera adapter. TeleVue NP-101, TV-102, and Renaissance-102 scopes require both a 3" and a 2" extension tube in front of the camera adapter to reach proper photographic focus, so some experimentation may be called for to see if this tube alone is long enough for use with your particular telescope focuser.