An improved system for attaching devices to the distal end of endoscopic instruments is described. An attachment adapter comprises a distal stop, such as a complete or partial loop or cylinder, which limits the penetration of an endoscope into the adapter. The adapter has at least one flange protruding proximally along the endoscope. The adapter is secured on the endoscope by a securing means, which compresses the flange or flanges sufficiently to provide a friction fit. The flexibility of the inventive adapter system allows the adapter to work reliably with endoscopes that are used, damaged or repaired. The adapter may further provide a slit or window allowing viewing of the vessel wall by a lens on an endoscope, thereby improving the operator's ability to understand the location of the endoscope during operation. The adapter may carry any of a variety of devices, including devices for closing a surgical incision, or treating or manipulating tissue. Improvements are described in a number of areas to allow more flexible pairing of particular endoscopes or endoscopic instruments with devices to be carried on their exteriors, while maintaining a tightly locked position of the external device on the carrier.