A windlass tourniquet for controlling severe limb bleeding.

Improvised tourniquets — a belt, a strap, a bandana and a stick — mostly do not work. They cannot be tightened enough and they slip. A purpose-built windlass tourniquet can.

This is for arterial bleeding from an arm or leg: the injury where the clock is running in minutes.

Two things matter. Keep it somewhere you can reach one-handed, and learn to apply it before you need to — correct application is tighter than people expect and it will hurt.

Carry one per vehicle at minimum. They are cheap next to the alternative.