Do not fit smooth-shaft bats to set-screw pawls
First-generation mechanisms clamp the shaft with a pointed set screw that sits in a recess on the old bat shaft. A modern smooth-shaft bat has no recess; the screw raises a burr that wedges the pawl and shaft together for good.
Systems
Related tips
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)