Abstract: A self locking and unlocking clamp for use in cooperation with an automatic fastener driving tool. The clamp includes a fastener receiving head having a pair of jaw members pivotably mounted thereto. The jaw members are operated to securely hold individual fasteners along their central axes while they are being attached to or driven into a workpiece. A trigger assembly and a cooperating locking assembly is provided on the clamp for (a) locking the jaws together in order to securely hold successive fasteners relative to the tool, and (b) unlocking to enable the jaws to move apart and thereby release successive fasteners once they become securely attached to a workpiece.