We use a bruce with ours, as we found the danforth supplied as part of ribcraft's anchor package didn't hold as well as we wanted
!! Will check the size at the weekend - think it's 5kg, and it fits ok. You may well be planning to do so, but suggest you line the locker with a cheap rubber floor mat to prevent the anchor taking chunks out of the grp when you're bouncing around - especially if you do go for a danforth or CQR with their more pointed flukes.