and extends radially outward therefrom so as to be in engagement with a portion of the bal seal adaptor 22 that is disposed adjacent to the second groove g 39 the true arc ring 26 is of sufficient diameter that it also serves to hold the bal seal 23 toward the shoulder in adapter 22 and this keeps the seal 23 from sliding off of the bal seal adaptor 22 when the later is moved in a cylinder 27 the pull rod 21 is preferably made from commercially available precision stock and requires only the machining of grooves and in some cases through holes the bal seal adaptor 22 provides an increased diameter to form part of the piston means the adaptor 22 provides proper sizing for the bal seal 23 itself and is appropriately sized to be sealed to the pull rod 21 by way of the 34 o 34 ring seal 24 furthermore the bal seal adaptor 22 serves as a capture device at one end for the split ring retainer 25 the split ring retainer 25 is suitably designed so as to accomodate a high shear force the true arc ring 26 functions to position the components and retain the bal seal 23 positioned on the shoulder of the bal seal adaptor 22 the present invention is usable as a piston cylinder construction either single or double acting the cylinder size.