I've searched far and wide and can't seem to find a parts list for this shifter. I've lost the bolt and need to purchase another. It is the right-hand (rear) shifter, for an 11-speed Shimano XT group.
From Shimano's Technical Documents website comes this exploded view of your right shifter. Typically on these drawings, Shimano will give the size and length of any fasteners highlighted in the drawing (see the "Clamp Bolt" listing--#8--in the linked schematic), however the entire base cover with it's screws is one part number and no information is given about the screws themselves. As has been typical of these kinds of shifters over the years and different models, the bottom cover utilizes two and even 3 different size screws in one unit.
Your missing screw is part of the assembly listed as #3 (of the referenced exploded view) and carries part number, Y06M98030, the R.H. Base Cover Fixing Screw Unit. I googled, "Shimano part number Y06M98030" (without quotes in the search query), and this is the most relevant link that wasn't the same Shimano site I linked above. Still nothing about the size, but you can get a good look at the threads and the shoulder of it. My final answer is that it's an M3 about 5mm long. Because of that shoulder, a matching fastener won't be easy to find in the local hardware store, but I wouldn't be put off trying an M3 socket head cap screw, short as I could get (though a Dremel with a cut wheel could customize a longer one) and seeing if that would be a satisfactory substitute. Or, obviously, the part is for sale.
1I purchased an assortment of small metric screws and indeed, turns out that an M3-8mm SHC seemed to do the trick. Technically, with the information you provided, I could order the screw (albeit as part of an assembly). Thank you. Nov 12, 2020 at 17:17
Incidentally, I think the SHC is a better fit than the original screw -- and I can get it at any hardware store. Nov 12, 2020 at 17:19
You’re in luck! Here’s a photo of the underside I grabbed, back when I was selling a M7000 shifter myself.
Can you see fine bolt threads inside the hole? If so, it’s going to be either M2 or M2.5, possibly M3. If the missing bolt obviously screwed into the silver mounting bracket, it definitely isn’t a wood screw.
It appears to be the same screw as the bottom left-most in my photo, so if you remove that one, you could compare. On the XT and XTR shifters, all of the fasteners are coarse threaded (much like a wood screw’s threads). If you discover that it is indeed a coarse threaded fastener, simply find one that screws into the hole with a reasonable amount of force (a screw that isn't too wide or narrow). Also take into consideration the length of the screw: you don't want it bottoming out.
If the missing bolt ends up being a fine threaded machine screw, put some threadlock on it before installation. If it’s a coarse threaded wood screw, don’t use threadlock, it’ll degrade the plastic.
Hey, thanks for the photo - I really appreciate it. The cover bolt (bottom right) doesn't seem to fit for me in the mount position (maybe not long enough). Nov 10, 2020 at 15:23
@SteveJ what about the bottom left screw? Nov 10, 2020 at 16:26
Intuition would suggest it should work, and indeed the bottom left is longer, but it just slips into the hole -- suggesting that I need the next size up (or that I'm really stripped : ). The thread on those is fairly coarse, which may narrow down the search. Nov 10, 2020 at 18:30
@SteveJ If you are sure the missing screw is not a fine threaded machine screw, then just use any old wood screw that fits. I suspect it screws into the silver bracket though - hence why I’m not sure. Nov 10, 2020 at 19:30
I was missing the Y0GV98030 for SL-M7100 SLX shifter. Pretty much the same bolt. Always out of stock everywhere.
But... Just ordered a Y06N98030 and it's done the job perfectly. So guessing the Y06M98030 will too.