Dan, i am the one that asked the "nuts/bolts" question...
 
as a very amateur vw owner...i rely on manauls, blog, and trusted website instructions for repairs so those instructions they actually say "use a 15mm wrench...use a 17mm wrench" depending on which repair you are doing.
 
in my limited time working on my '87 vanagon...i normally see 13mm, 15mm, & 17mm nuts/bolts.  but i am sure others in the group can add much more insight.
 
jabin
1987 VW Vanagon Transporter
 

> Date: Tue, 20 Dec 2011 01:16:12 -0800
> From: d.rotblatt@VERIZON.NET
> Subject: Most common Nuts 'n Bolts?
> To: vanagon@GERRY.VANAGON.COM
> 
> The thread on where to get nuts and bolts made me think - What size bolts are the most common in the VW? I also have a spitfire, and 90% of the bolts are 3 different sizes (1/4, 5/16, 3/8 fine thread std), so I bought a supply of all of them in different sizes just in case. It's a pleasure to have them around when I need them - worth it just in gas money. I'd like to do that for Van Winky. So...what sizes of bolts are handy to have in the old tool box, or does VW not standardize their bolts and it's just not worth it?
> 
> Dan
> Los Angeles, CA
> "Winky" the '85 Westy Weekender