I feel that the Honda engineers could have trimmed it down to 2 different bolts. There doesn't really seem to be any necessary differences between the bolts other than shoulder/non-shoulder. It would certainly simplify buttoning the Tupperware back up!
The Honda bolts for the fairing are usually 5mm or 6mm. The shoulder is crucial and specific to the location.
The bolt isn't there to clamp the fairing to the bike. It is there to locate the fairing in position, hold it there and prevent it from falling off.
The shoulder is exactly the right diameter for the hole, and the shoulder length is either identical to, or fractionally greater than the thickness of the plastic fairing at that point. When you tighten the screw, you should be tightening the shoulder against the frame or captive nut - not against the plastic.
If you use a bolt without the correct size shoulder - eg no shoulder, or a shoulder that is too short - then you will be tightening the pan head against the fairing, and the final tightening force will try to twist the plastic under the pan head. This will quickly cause the plastic to crack around the hole .
6mm screws are used for the heavier loads - eg above the cylinder head - but also it seems, to avoid confusion. The side panel for my 2009 model for example has 2x5mm screws at the front end and 1x6mm screw with a longer shoulder at the rear where the rubber button of the pannier locates. But I think my 2006 model had 3x5mm screws - one with a larger shoulder. Easy to put them in the wrong place.
The 6mm bolt without the shoulder is also used on the fairing - eg the rear mounting points for the grey lower fairing under the footrests. This bolt doesn't need a shoulder as the metal heat shield that is fixed to the inside has a metal sleeve attached, that does the same job.
Ditto for some of the mounting screws for the front fender. The captive nut provides the sleeve that prevents the screw from tightening against the plastic, so no shoulder is provided on those screws.
There is a similar arrangement for the clutch lever pivot bolt. This has a long shoulder, which tightens against the thread in the lower half of the lever. If it didn't have this, tightening the bolt would squeeze the two parts of the bracket together and either clamp the lever tightly, or (more likely) one of them would snap off. In fact the bolt shouldn't be tightened at all. The torque is something like 2Nm. The nut is a lock nut to prevent it from unscrewing.
At the end of the pdf attached to post#1 of this thread, I have photos, descriptions and part numbers of the various screws and clip used on my UK ST1300 A9
A set of notes about putting the fairing back onto the ST1300. It covers most of the fitting gotchas, which might otherwise catch you out and/or result in broken tags. Also lists all of the fasteners - photos, description,, part numbers, where they fit and why it matters. Very useful for...
www.st-owners.com
