2 Magnesia Soldering Blocks For Soldering Jewelry & Fine Welding. This is a new set of 2 magnesia soldering blocks. These two blocks are made of a soft, fire proof magnesia material. These are great for holding pins or small work pieces, soldering and fine welding. The blocks can withstand temperatures of up to 2000 F (1093 C). Each block measures approximately 6" x 3" x 1 1/2" (152 x 76 x 37 mm).