I was taught to use 3/9 to avoid misdiagnosing worn ball joints as wheel slop, and to use a light touch at 3/9 and watch the tie rod while you do it to sense wheel movement without steering movement.

Here's an on the road diagnostic for idler arm play. Worn idler bushings put slop in the pside wheel steering, and NOT in the dside. The pside tire will toe slightly out while driving forward. As you start a mild turn to the left, that tire will resist the turn, then flop into the turn, causing a mild dart to the left. Truck will pull slightly to the right when going straight. Steering slack feels looser in right turn direction that in left turn direction. Slack is abrupt to the left, and has increasing resistance as slack to the right is taken up, if measured while moving in a straight line.