Plug welded joints are used-

Plug Weld or slot weld: It is used for attaching flat plates using one or more holes or slots in the top part and then filling with filler metal to fuse the two

The effective area of the plug or slot weld is generally equal to the area of the hole or the slot being welded This is applicable for the load putting the

slot pragmatic bet 100 The short answer is the larger the plug the easier it is to weld If you are not given specifications then I would use a 1 diameter hole through the 12 sheet

slot thunderstruck ii fiable Plug Weld or slot weld: It is used for attaching flat plates using one or more holes or slots in the top part and then filling with filler metal