Usually, hardtops do not have central kernels.
The Hardtop ("hard roof") was originally a type of car body in which the roof could be removed. Unlike other convertibles, these models have a completely rigid roof, and can not be stored in the trunk.
Of these convertible Hardtop there are two varieties: the Detachable Hardtop (convertible), and the Retractable Hardtop Roofs (retractable).
There are also coupes and sedans without pillarless hardtop, cars that resemble a convertible because there are no "b" pillars, or central sides, so the roof rests on those of the windshield and partly the rear body. This is easily noticeable when opening the doors with the windows down, that do not have a "frame" that surrounds the glass when it is above, but the glasses close directly on the ceiling. Pontiac Catalina 1963, a classic Hardtop that shows details in the awning that resemble it to a convertible.
In the mid-70's, given the new safety regulations for cars in the United States, it became very difficult to make hardtop cars, so they stopped being built in this country, leaving only some models of BMW, Mercedes- Benz, Toyota and Nissan as later representatives of these vehicles.
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