I think its 11mm but goes into rail too far the 14mm adapters look better design as not tappered , if the 11mm ones were same shape as 14mm they would work
The adaptor that they came with fit ok i std rail but not in the sard rail i have in the car , anyone know where to get some adaptors to suit the sard rail ?
R33 GTR / 34GT Clutch , i would say no more than 15k kms at most , i replaced with nismo twin but would be good base for rebuil for hi hp or use as is on lower hp car .