Apparently Nissan changed the clutch fork design from 2003 for 2004+. The newer fork is cast and much stronger.
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Question: If my Z is a 2004 but was manufactured in 10/2003, is there a possibility that it has the older design?
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(I'd crawl under and look but it is raining here today)
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7/2003 was the cut off for the stamped steel fork. The cast fork began showing up 8/2003> production. Doesn't mean yours is cast, Have to look to be sure.

 

Link to upgrade kit we offer.
Heavy Duty Cast iron clutch fork kit