Here's my collection of metric and inch feeler gages, and a metric micrometer:
I've used them all at one time or another doing a valve clearance inspection and adjustment (shim R&R) on my 91 ST1100.
I have to admit that it took a while for this lesson to sink in:
Don't bother with metric feelers because Honda
shim thickness intervals are 0.025mm and .001"=.0254mm... close enough for our purposes. In other words, use the inch specs for your ST's intake and exhaust valve clearance, and measure with inch feeler gages. Then for every .001" that you want to move your valve clearance (either tighter or looser) select the next size shim (either thicker or thinner) from the one currently installed.
For the ST1100, you'll need feeler gages from .004" thru .012". If you're really anal, add a .003" and .013", but hopefully you won't ever find a valve a whole 2 thousandths out of spec. I don't know the clearance specs for the ST13, but I have heard the range of shim sizes installed is somewhat different than the ST11. I've attached a list of all the Honda shim sizes, markings, and part numbers.
BTW, there is a very nice loaner ST1100 valve clearance/shim R&R kit available through ST-Riders. Details here:
http://www.stocrallies.com/st-riders/index.php?topic=556.0
Also, my friend Dan Horton, STOC 1256, made up a nice shim calculator spreadsheet for the ST1100s, if you'd like to confirm your simple math.
[edit: if you can't find bent feelers, buy straight ones and bend them yourself.]
[edit2: My friend Ray Stevens, STOC 1014, made a nice shim R&R layout sheet.]
HTH
John