Valve cover bolt head size 3.9 L V8

[Neo]

I've noticed on my 1996 Discovery 1 that one of the valve cover bolts is loose however I don't have a socket to fit it. So what size and type of socket do I need. It looks like a bi hex socket head. But I'm not sure.

[trout1105]

8 mil I think

[bee utey]

8 mil I think

Correct. Double hex sockets aren't all that common but you'll find one eventually. I bought mine from the UK via ebay. Needs to be 1/4" drive. Sometimes you can tighten the outer bolts using a small ring spanner, 5/16" is the same size.