Tim Arnold suggests solving your loose playfield screws problem by replacing
them with bolts. He suggests using 2" #6 studs. Drill a 1/8" hole, from
the top side. Be careful of items you may run into on the underside while
drilling. If there is too little room on the underside use a flat head bolt
and countersink it, so it is flush with the bottom and out of the way.
Tim Arnold pinGame journal, #25 September 1993 pp 37-38.