how can you tell when connectings rods need to be replaced

[XSLeo]

There are two specs on the connecting rod, One is side play, you move the rod sideways and mearure the clearance with a feeler gauge. On the 70-77 engines the Clymer book calls for .012-.024 clearnce, 78 up .006-.016.
Thwe two mm spec is rocking the rod on the bearinghs without moving it sideways.
Page 93-94 in the Clymer book.
Leo