We have developed a prototype system to support the repair and assembly of mechanical watches using smart glasses with AR functions. The proposed system displays a translucent image from a stereo camera in the center of the screen of smart glasses. By shooting small parts at hand with a stereo camera, the operator can see the surrounding scenery through the glasses and a magnified 3D image in the center of the screen at the same time. To evaluate the effectiveness of the proposed system, some fundamental experiments were conducted. Several subjects first performed a handling task of very small screws with the naked eye, with a binocular stereomicroscope, and with the developed system using binocular stereomicroscope images in order to investigate technical issues. We also conducted experiments using two smart glasses, an old system with a larger video delay and a new system with a smaller video delay. As a result, it is revealed that both the work efficiency and the stereoscopic effect decrease if video delay occurs in the magnified image. It is also revealed that it is difficult to feel the sense of distance by the smart glass systems because the actual scenery and the magnified image which subjects can see at the same time represent spaces with different scales. Finally, it is investigated how the stereoscopic effect changes by changing the convergence angle from 12° to 20° in order to obtain a guideline for determining the convergence angle of the small cameras whose sizes fit a hand. As a result, the contradictory results were obtained that the subject's sensitivity in the depth direction was high when the optical axis of the camera was about 12°, while the subjective stereoscopic effect was highest when it was 20°. It is necessary to consider the way to use the system to determine the convergence angle.