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This angled slot is factory on all oversize WL (45") pistons.
Standard bore (2.745 std. size) pistons do not have this slot.
The slot is only on oversize pistons.
This piston (pictured) is +.040 oversize.
The slot is only on one side of the piston - Not both sides.
Slot position is towards the front of engine(opposite thrust face)
The thrust face of a piston is on backside of each cylinder.
Correct installation = slot towards front-side of cylinder.