could anyone tell me the size of the nut for a cossie head and if it is a female torques??

 

its a 12mm spline drive, it isn't torx, but buy a good one as if they strip the bolt I would hate to try to drill one out.

edit, sorry this is for standard bolts have never had arp studs but they look like normal hex heads to me.

 

normal 12 point socket, can't remember the size though

 

14mm 12 points longue