Stephen,
Thanks for your response. Yes, the plates would appear to be like those in your photo. However, from a photo taken earlier in the year, it would appear that the drum on Tarakihi has probably been fitted with a "turnbuckle" kit as it has plates external to the drum that are shaped and tapered to a single hole fixing. As I haven't been able to get to the boat recently, I can't say if there is a bottle-screw within the jaws of the plates but I don't think so. Our forestay was a bit slack this season (used the backstay tensioner to keep it tight as possible)so perhaps the wrong fixings were originally supplied and my 5-holed plates were a replacement!
Regards
Chris Cobb
235/48 "Tarakihi"