Socket welded connections are a type of welded connection where there is a male component that slides into a female component and then a fillet weld is made between the shoulder of the female component and shank of the male component.
Please refer to ASME B16.11 for typical dimensions and details.
A male socket welding end does not normally have any reduction in outside diameter. The outside diameter is constant and a fillet weld is used. The official dimensions for socket welded components would be specified in ASME B16.11.