Borescopes and videoscopes are widely used in many applications to exam and inspect hard to see areas.
High end videoscopes are usually articulating borescopes with small diameter (less than 6mm), where the small probe tip can be bended or rotated to see different directions.
Classified by viewer type:
USB to PC/Mac/Android
Wireless to Android/iPhone/iPad
Classified by insertion tube: Rigid, Semi-Rigid, Flexible
Insertion tube and probe diameter: 2.0mm, 2.4mm, 2.8mm, 3.0mm, 3.9mm, 4.0mm, 4.5mm, 5.0mm, 5.5mm, 6mm, 8mm, 10mm, 12mm