The clot formed after coagulation cascade is not stable unless extensive cross linking occurs .this is done by

Ref Robbins 9/e p119 Thrombin is the principal enzyme of hemostasis. It catalyzes the conversion of fibrinogen to fibrin and activates procoagulant factors V, VIII, XI, and XIII. Additionally, when bound to thrombomodulin, it activates protein C, an anticoagulant zymogen