Do these sections come pre-welded or do I need to weld them together?

These are individual straight sections. You'll need to weld, clamp, or use band clamps to connect them based on your system design and permanence preference.

Can I use these sections for a cat-back exhaust or do I need additional components?

These are tubing only — you'll need a manifold or downpipe, muffler, resonator, or other components depending on what you're building. This kit gives you the backbone piping to route between major parts.

Will I need to paint or treat the steel before installation?

Mild steel will surface rust over time if exposed to moisture. Many builders apply high-temp paint or ceramic coating before install, or leave it bare if tucked under the vehicle and draining well. Your choice based on aesthetics and environment.