For insulators used in AC lines, the shapes of porcelain and glass disc-type suspension insulators can be divided into standard (common), bell-jar, 

and outer shed types. Among them, the outer shed type can be further divided into double shed, triple shed, and aerodynamic types. 

The most common shed types of insulators for conventional lines are standard, bell-jar, double shed, or triple shed.

Standard or conventional insulators typically feature ridges under their sheds,

 which serve to increase the creepage distance of the insulator and thereby enhance the flashover voltage. Conventional insulators have shallower ridges, 

while bell-type insulators have a deeper outer shed skirt and often have ridges in the middle that are deeper than those on the outer shed. Outer shed insulators do not have ridges under their sheds.