Special Features:

Drawing describes as swing prism borescope

Properties:

A viewing device used to visually inspect items such as cannon bores, internal combustion engine cylinder walls, propellant perforations of rocket motors or similar items, for defects of manufacture, corrosion, scars, erosion, etc., without the necessity of disassembling the item(s). It may or may not have extension tubes to cover the various ranges of inspection. The item is basically a straight-tube telescope using a mirror or prism.