Abstract: A PEX crimping tool includes four rigid links pivotally coupled together in a modified four-bar linkage arrangement. The first link has a first jaw with semicircular work face, a first handle and an elongated slot between the jaw and handle. The second link is pivotally connected with the first link at a first pivot and includes a second jaw with semicircular work face. The third link is pivotally connected with the second link at a second pivot and includes a second handle remote from the second pivot. The fourth link has a first end pivotally connected to the third link at a third pivot and includes a second end connected to the first rigid link so as to swing and move with respect to the first link about a fourth pivot movable along the elongated slot. The tools are designed to crimp ASTM F 1807 rings.