Ok, the bases are frequently seed as following types in current market:

Screw Bases
Lamps with screw bases have one lead-in wire soldered or welded to the center contact and the other soldered or welded to the upper rim of the base shell. Base shells are typically made of brass or aluminum.

Ceramic Bases
Ceramic bases have internal leads welded to either metal contacts or external lead wires.

Fluorescent Lamp Bases