A tourniquet is built to stop severe, life-threatening bleeding from an arm or leg by compressing the blood vessels above the wound tightly enough to cut off blood flow entirely. It's meant for extremity wounds, like gunshot wounds, deep lacerations, or traumatic amputations, where direct pressure alone isn't controlling the bleeding fast enough. It's not effective for wounds too close to the torso to compress, like the neck, chest, or groin, which need a different approach like wound packing or a chest seal.

Windlass tourniquets, like the C-A-T, SOF-T, and TMT, use a rod or bar that's twisted to tighten a strap around the limb, then locked in place, and they're the design most training programs teach and the CoTCCC-recommended standard for extremity bleeding. Elastic tourniquets, like the SWAT-T, use a stretchy band wrapped tightly around the limb instead of a rigid mechanism, which lets them adapt to limb sizes a windlass strap can't accommodate. Ratcheting tourniquets tighten through a buckle mechanism that clicks into place incrementally as the strap is pulled through it, rather than requiring the repeated twisting of a windlass, though they're less common than windlass or elastic designs.

The C-A-T uses a polymer windlass and a hook-and-loop strap, and it's the tourniquet most training programs teach, with the most documented field saves of any windlass design. The SOF-T Wide uses a machined aluminum windlass and a fully mechanical buckle instead of hook-and-loop, which holds up better in wet, muddy, or sandy conditions where Velcro can lose grip. The SOF-T Wide also folds down smaller than the C-A-T, though the metal windlass makes it heavier.

The SOF-T Wide is a common choice for everyday carry because it folds down smaller than the C-A-T, which matters more for a pocket, bag, or low-profile carry than the small weight difference between the two. Its all-mechanical buckle also means there's no hook-and-loop to collect lint or debris from being carried loose day to day.

The SWAT-T is generally the better option for a child's limb, since its elastic design can tighten down to a circumference most windlass tourniquets can't secure. Research on pediatric limb models found that standard windlass tourniquets can usually be secured on children around age five and older, but become less reliable on smaller, younger limbs, while the SWAT-T's stretch-and-tuck design was able to secure on most simulated pediatric limbs across that same range.

The SWAT-T is also the more practical choice for a dog, since a dog's leg doesn't have the relatively uniform, cylindrical shape a windlass tourniquet strap is sized around. Its elastic band adapts to a dog's smaller or more irregular limb shape in a way a fixed-length windlass strap often can't, which is part of why it's commonly recommended for K9 handlers to carry alongside their own kit.

A standard tourniquet works by compressing a limb between the wound and the torso, which only works where there's a bone to compress against. Junctional wounds, like the groin, armpit, or pelvis, sit too close to the torso for a standard tourniquet to work, which is what specialized devices are built to address instead. These are advanced, more expensive devices meant for a specific wound location and typically require dedicated training, not a routine addition to a personal IFAK.

Most tourniquets don't have a hard expiration date the way hemostatic gauze does, but the band, buckle, and windlass hardware degrade with UV exposure and heat over years, even sitting unused. The tourniquet you actually carry shouldn't be the one you practice on: a dedicated trainer, usually sold in a different color, absorbs the repeated twisting and buckling so the live device stays in reserve for the one time it actually matters. Manufacturers generally recommend replacing a carried tourniquet after several years of exposure to a hot car, direct sunlight, or other harsh conditions, regardless of how little it's actually been handled. If the band has visible cracking, stiffness, or fraying, it's time to replace it regardless of age.