3) Plug Weld and Slot Weld
A plug weld is a weld made in a circular
hole in one member of a joint fusing
that member to another member. A slot
weld is similar to a plug weld except
that the hole is elongated. See Figure
3.6.
In preparation for plug and slot welds,
holes or slots are made in the upper
plate. On relatively thinner material,
such welds can be made without holes
or slots and are called arc spot and arc
seam welds, in which the upper sheet
is melted and fused to the lower sheet.