The steel bracket is made from 10-gauge steel. This means you need to use hardened steel drill bits. We can also drill them for you at a cost. A 3/16” bit is enough when using #8 screws. However, you are using the steel bracket because you need more holding strength for the connection of male bracket to the wall. So you would also be using lag bolts to achieve that. This means that you need drill bits that correspond to the size of the lag bolt that you want to use.
Most customers now use longer lag bolts to attach the female bracket to the shelf as well. The same theory applies. You need to have the corresponding drill size, which fits the lag bolt you are using.
The steel brackets do not have a die line to indicate where to drill the extra holes. As long as you do not drill the holes too high or too low, you can drill as many as you want, wherever you want.
Please refer to the below diagram as reference: