Triumph Exhaust Pipes /Pair High Level Cross over 1 3/4"ID at cylinder head to fit over the stub is 1 5/8"42 mmOD at cylinder head is 42 mm 1 3/4"OD at the silencer end 1 3/8" 35 mm650ccm Unit / 500ccm swing Arm 650 Pre Unit Made in EnglandPlease look at all pictures