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The joining of metal components by a localized fusion is a technique used with a number of arc welding processes; it can be accomplished with both manual and mechanical procedures. Early applications used the older, established processes of bare metal arc welding (with light flux-coated metal electrodes) and submerged arc welding. With these processes, welding was predominantly limited to the heavier gages and thinner plate thicknesses. In some cases to insure penetration, the welding was done through a prepared hole in the upper member of the joint; this is commonly referred to as plug welding. Although arc spot welding using the above-mentioned processes was not extensively used as a prime process, it was used for repairs and for tacking components together to hold them in relation for subsequent processing. Later process developments of gas tungsten-arc welding, gas metal-arc welding and gas metal arc flux-cored welding have greatly extended the application of arc spot welding. These more recent process developments allow arc spot welding of metal thicknesses of from 0.005 in. to heavy plates J/8 in. thick. What process is best suited for a specific application depends on the material being welded as well as the metal thickness and joint description.