This set replicates a special M2 machine gun tripod mount used on HMMWV gun trucks during early OIF (Operation Iraqi Freedom).
You can find in-action pictures and more info about this mount in this forum thread at Armorama.com
http://armorama.com/modules.php?op=modload&name=SquawkBox&file=index&req=viewtopic&topic_id=165971&page=1