An apparatus and method are provided for reducing the width of a plurality of longitudinal slots or other openings spaced circumferentially around a slotted tubular member. The invention includes a seaming roller positioned to contact the outer surface of the slotted tubular member for transverse movement across the plurality of slots, and adapted to apply a force onto the slotted tubular member so as to reduce the slot width. The width of the plurality of slots is detected and compared to a set value indicative of a desired end slot width and based on this comparison, an adjustor connected to the seaming roller, adjusts the force applied by the seaming roller to the plurality of slots. Each opening is adjusted by the seaming roller to have a profile with a width that throughout the length of the slot profile, varies no more than a given tolerance from the desired end slot width. The invention also provides a slotted tubular liner comprising a metal slotted tubular member formed with a plurality of longitudinal slots ≦3.175 mm in width spaced circumferentially around the member, each slot having been cut and then transversely seamed to have a profile with a width tolerance, that throughout the length of the slot profile, varies no more than +/−0.0127 mm, and preferably varies no more than +/−0.00762 mm from a desired end slot width.