Alfa bolts are metric, so you're going to want to start using the other side of that ruler. Also bolt length is measured from the bottom of the head.
It looks like that's an M8-1.25 x 55 in 5.3 strength, but verify the measurements as I'm estimating by measuring the picture. Assuming I'm correct, McMaster-Carr has an equivalent (8.8 instead of 5.3 but that's fine) as 91280A548 for $9 for a pack of 25.