Glass Tube Fuses which are safety components used to protect electrical circuits from overloads and short circuits. 

Function: They protect circuits by interrupting the current flow when it exceeds the fuse's rating. 
Size: 5x20 refers to a 5mm diameter and 20mm length. 
Ampere Ratings: Available in various ratings, from 0.5A to 30A, as shown in the image. 
Usage: Commonly found in electronics, appliances, and older vehicles. 
Replacement: Always replace a blown fuse with one of the same type and rating. 
Breaking Capacity: Glass fuses have a lower breaking capacity compared to ceramic fuses. 
Visibility: The glass casing allows for easy inspection of the fuse element. 
Safety: Using the correct fuse rating is crucial for safety; incorrect ratings can lead to damage or fire.