Abstract: A ride-on turf mowing machine rollover protection assembly consisting of a mower chassis having left and right main rails and having a plurality of cross rails spanning between the left and right main rails; left and right upwardly opening quills; a first plurality of welds rigidly interconnecting the left main rail and the left upwardly opening quill; a second plurality of welds rigidly interconnecting the right main rail and the right upwardly opening quill; a roll bar having left and right legs, each leg having a lower end, the lower ends of the left and right legs being respectively closely fitted for nesting extension into the left and right upwardly opening quills; and a plurality of helically threaded bolt, nut, and double shear eye combinations removably mounting the lower ends of the left and right legs of the roll bar within the left and right upwardly opening quills.