Using a MICROWAVE PRIMARY COIL for a home-made spot-welder.
Typically these have 2 input terminals/wires that you connect your black & white ac plug wires to.
Mine has 3 INPUT TERMINALS/WIRES.
Do not know which to connect to black/white plug wires.
Transformer = SAMSUNG SHV-U1870C

 

This service manual for a Samsung microwave which uses a SHV-U1870B includes a schematic which might help. The different connections appear to be for different output powers.