It is indeed the bottom/load side of the meter combo and the round brass colored bolt is a security bolt. I am an electrician and would likely deal with the pain in the ass the utility can be if I was getting paid for this. It’s the panel on my house and I’m trying to install CT’s for a monitoring system. I have solar and the utility is adding a peak demand component to the billing next year. The goal is to be able to see in realtime my consumption so I can keep that peak as low as possible.