A few of Dowel Pins is too loose or drop off --> The fitting clearance between hole and dowel pin is not enough--->The actual hole size shift to upper side of specification(Ø5+0/-0.01)--->The size of hole was to get bigger by reaming after machining(Reaming is being used for assure the precision of Ø5+0/-0.01)---> The operator of reaming is not practiced for aluminum alloy.