M5 Wingbolt - sold individually
The d-rings that come with Silver shifters are perfectly good but I find that these are 10% easier to turn and look 75% cooler. They're more likely to scratch your hand if you slip tho, so don't buy if you're the litigious type.
Put some loc-tite on them and you'll likely never have to mess with them. If your shifter loses a little tension, turn it at the next stop or even while you're riding, if you're careful.
M5 x .8, 10mm long