I obtained a spare eyebolt from Bill Parker some years ago.
To me, it looks a little smaller than the ones actually fitted on my boat, but is 12mm (marked "M12") thread, "SWL" and "0.4T" ((I think "safe working load. 0.4T"; vertical load I think?). Other marks are "CE" and "TI". I am not an engineer, but I believe it is not stainless.
I can see no information in the Owners Manual, and in order to make progress I have located a product that looks the same at least! It is from RS Components and their product description is : "high quality, metric eyebolts with collar to BS4278 for use in a wide range of lifting applications. These eyebolts are proof tested and supplied complete with test certificate".
Since we do not have a lot of information, I thought I would chance it, and I have ordered two from RS Components Ltd, (Birchington Road, Corby, Northants, NN17 9RS) that I think are replicas of the one sent to me by Parkers(famous last words...!). Delivered cost for two is £12.43.
UPDATE: The eyebolts arrived in less than 24 hours. Well packaged, with certificate, M12 BS Collar Eyebolt, BS4278; 400kg maximum safe working load (SWL). To my eye, these new replacement bolts do look pretty much the same pattern as the one supplied to me by Bill Parker in 2007.
John Tanner P235/34