Pretty good endoscope, but if you're buying because you need to inspect a rifle barrel, you should buy NTS150B rifle barrel borescope from Teslong , not this NTS150RS endoscope.
On the NTS150RS endoscope, the focal length is not optimal for smaller bore rifle barrels. It's nice to be able to see every inch of the bore, but the focal point is further down the barrel so the area right in front of the camera is not in focus. But the small diameter of the camera, after removing the thread protector/shroud, is small enough for the popular .223/5.56 barrel bore. That said, the attachments that thread onto the camera in place of the thread protector do not fit in that size bore. The NTS150B has a much shorter focal length designed for inspecting rifle barrels.