It is a 4-piece type N1 muffler that best fits with Aero Bumper, Rear [71501-AP1-001].
Main pipe 60.5φ → 50.8φ
Main silencer 152φ
Rear silencer 127φ
Exit diameter 65φ
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Remarks & special notes
The AP1 early model genuine rear bumper can be installed with small processing (unpainted part cut).