Borescope is a rigid (industrial endoscope) or flexible (fibrescope, flexible borescope) tube with an eyepiece on one end, an objective lens on the other linked together by a relay optical system in between. Borescopes are used for inspection work (borescope inspection) where the area to be inspected is inaccessible by other means. There is 2 main types of borescopes. Flexible borescopes also are called Fiberscopes - because their relay optical system that trasfer image consist of thousands of tiny fibers (fiber optic image bundle). Rigid borescopes (bore scope) are similar to a fiberscope, but have a higher quality image and are not flexible. Rigid borescopes are therefore better suited to certain tasks such as inspecting automotive cylinders, fuel injectors, hydraulic manifold bodies and gunsmithing. Rigid Borescope on sale or flexible fiberscope may be fitted with a magnifying device and a way to illuminate the work being inspected, usually illumination fibers contained in the insertion tube of the borescope. The eyepiece may be fitted with a coupler lens to allow the borescope to be used with imaging devices such as a video cameras for borescopes. Borescopes can be used for rifle inspection and precision shooting as well.
You can find additional information and/or buy these devices here: http://www.fiberscope.net/