Will these zip ties hold under constant heat from exhaust wrap?

Yes. Stainless steel doesn't degrade or weaken under sustained thermal cycling the way plastic ties do. They won't melt, shrink, or lose tension as your exhaust temps swing between cold starts and full throttle.

Can I use these on anything besides heat wrap?

Absolutely. The 5mm width and 12" length work for bundling wiring harnesses, securing loose tubing, or fastening components where vibration resistance matters. Just keep in mind stainless steel won't degrade under UV or salt spray.

How tight do I need to cinch them?

Snug enough that the wrap doesn't shift under vibration, but not so tight you compress or crack the wrap material itself. You want pressure against the pipe, not crushing force on the wrap layers. Hand-tight usually does it.