Nvinfer parameter:threshold pre-cluster-threshold Post-cluster-threshold

In nvinfer, there are three parameters:threshold pre-cluster-threshold Post-cluster-threshold . I understand that preClassPrecluster before clusting (such as cluster mode=2: nms), Post-cluster-threshold after clusting. For example, the bbox confidence in yolov5 lesser than pre-cluster-threshold would be rejected, then Comprehensive probability = the bbox confidence * the class probability. the comprehensive probability lesser than Post-cluster-threshold would be rejected. So what is this parameter threshold used for? Does it overlap with Post-cluster-threshold ?