Plug welds and slot welds are identified by the same symbol, except

Plug welds are essentially round welds that are made inside an existing hole, most commonly in one piece of metal The purpose? To weld that

Slot or Plug Weld · Width or diameter of slot should not be less than three times the thickness of the part in which slot is formed or 25 mm,

plug slot plug weld is its diameter whereas the size of a slot is its width They may be completely filled or filled to a depth specified within the weld symbol See

plug slot weld Overview of plug and slot welds, their uses, symbology and application