Trying to fill small holes can be frustrating but one of these makes it easier. Just hold against the back of the hole you are welding and the MIG will fill the aperture instead of firing yards of wire through the hole! The weld won't stick to the block, which is smooth on all sides so it makes contact with as large an area of the panel as possible. This dissapates heat away from the weld area, reducing the risk of distortion in your panel.
Everyone working with thin body panels should have one! Copper block 50mm (2") square made of high purity solid copper with radiused edges for easier handling.
C&B Tip: Don't confuse with those thin items with magnets inside to stick to the panel 'hands free' - they just collect steel fragments and then don't contact the panel for heat dissapation.
SAFETY: Wear welding gloves when holding! Conducts heat very efficiently INTO the block and away from the panel.