Unfortunately the TK4 is an ineffective design, which is too bad because it is a simple and compact design. CoTCCC removed it as a recommended TQ after it was removed from a study due to mechanical failures. I do not believe that a new version has been evaluated yet. It is no longer issued to US Military units.

The following is directive from Defense Health Agency following a study from Naval Medical Research Unit San Antonio LINK

The NAMRU-SA study demonstrated:

(1) the poor performance of the TK-4,

(2) the significant risk to the casualty and the First Responder due to catastrophic TK-4 failures,

(3) that the DoD is already moving away from this device, and

(4) that there are much safer and effective, CoTCCC-approved extremity TQs available to warfighters.

Remove tourniquet from all Service assemblages and dispose of per Service policy. Replace with CoTCCC approved tourniquet (CAT or SOFT-T tourniquet).
"Trust in God --and press-check. You cannot ignore danger and call it faith." -Duke