Question re hex bolt sizes on SKS mudguards

Critch Posts: 60
edited August 2013 in Road general
I've got a Lynskey Sportive Disc 2013 model and I'm trying to source decent mudguards for the incoming winter months. I've tried the SKS chromo's fixed mudguards but none of the hex bolts fit the threaded eyelets on my frame and forks...

Lynskey have told me M5 bolts should fit. The bolts that come with the SKS kit don't, none of them do. I can just get them started if I am firm with them but I know as soon as I stick in an allen key and begin to turn they will chew up either the the thread on the bolt or the the thread in the eyelet, which is not good.

Does anyone know what size the hex bolts are that come with these kits - I'm thinking imperial - metric issue, but these days that can't be right. Or is it an issue with the eyelets on my frame?