Will these zip ties hold up to direct exhaust heat?

Stainless steel handles high temperatures without degradation. The gold finish is corrosion-resistant, so they won't seize or weaken if exhaust condensation reaches them. They're rated for engine bay conditions.

Do I need anything else to secure heat wrap with these?

Just these zip ties — no additional fasteners or hardware required. They cinch down and lock without tools. Trim excess tail with scissors or a utility knife after tightening.

Will 12" be long enough for my wrap?

Depends on wrap diameter. Measure around the thickest part of your wrapped component — if circumference is under 10", one tie per section works. Larger bundles may need two ties stacked or side-by-side for even pressure.