plug weld and slot weld
8.4. Plug and Slot Welds
The types of welds used to create the weld joint can be categorized into various types, which are largely defined by their cross-sectional shape and the methods used to produce them.
The Different Weld Symbols Explained: Welding Basics
My slot weld call out was based on a simplistic definition that while fillet welds maybe be placed around the inside of a slot, if you completely fill the slot than a slot weld symbol would better describe the weld.
Welding Symbols - Types, Example Diagrams, Free PDF Charts
Even though they differ in appearance, the weld symbol that represents plug and slot welds is a rectangle. Due to the nature of these processes, this symbol cannot be represented as weld on both sides.