How can I tighten the bolt for the handlebar clamp on these levers? I managed to rotate them about the bar, and I need to tighten it so it doesn't move around when I'm riding. Do I need to undo the tape, or is there a bolt hiding somewhere under the shroud?

The exact model is 9-speed 3500, new Sora, if it makes a difference. Thanks in advance.

Can't tell by Shimano's exploded view diagram, but the clamp bolt will either be along the side, toward the inside of the bike, just under the rubber hood, or deep in the actual polymer assembly where you can get at it with an extended 5mm hex key, behind the shifter assembly when you have the brake lever pulled all the way back.

The exposed gear cable versions have the bar clamp bolt hidden under the hood. If you were looking at the RH STI unit from the front this bolt would be at about the 10:00 point, on the outside and just above the mid point. There will be a trough in the body disappearing under the rubber hood. A 5m allen a few inches long (don't use a ball ended one) will engage the bolt head. You'll have to feel around for the bolt head a bit.

The newer under the bar tape gear cable versions have the clamp bolt on the top of the body. Roll back the rubber hood a bit and you should see it. I find that a "L" allen wrench (5mm) which is cut down to only be about 3/8" long works well in the tight space. Andy.