Im not that familiar with the tool box or the bearing naming system or standards. So I had a question some bearings are straight forward they give OD and Bore size and thickness. So for these type of bearings in the image how do I determine OD diameter when they only give the bore size? So I need a 12 diameter bore with 24 OD 6 MM thick. How does the naming system in the front work what do the two front numbers mean?

They all have the 12 diameter bore what do the numbers in the front mean?