Sheldon says (http://www.sheldonbrown.com/headsets.html) that ISO (for 1" steerer diameter) headsets have 26.4mm crown race inside diameter and 30.2mm frame cup outside diameter.
I had assumed 30.2mm was the stack height- perhaps it is actually one of these: http://www.sjscycles.co.uk/product-Tange-Tange-Levin-1inch-Chrome-Steel-Cup-Threaded-Headset--33.3mm-Stack-Height--Fork-Seat-26.4mm--Frame-30.2mm-10953.htm
Maybe measure the stack height to be sure?
@Cupcakes started
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Sheldon says (http://www.sheldonbrown.com/headsets.html) that ISO (for 1" steerer diameter) headsets have 26.4mm crown race inside diameter and 30.2mm frame cup outside diameter.
I had assumed 30.2mm was the stack height- perhaps it is actually one of these: http://www.sjscycles.co.uk/product-Tange-Tange-Levin-1inch-Chrome-Steel-Cup-Threaded-Headset--33.3mm-Stack-Height--Fork-Seat-26.4mm--Frame-30.2mm-10953.htm
Maybe measure the stack height to be sure?