Short answer: Use these.
Longer answer: There are two options - threaded inserts or lag screws.
Lag screws are straightforward, but offer limited versatility for installs, disassembly, and shipping, and sometimes risk breakage in the tabletop itself. Threaded inserts provide a simple, clean option for consistent assembly and disassembly, while maximizing the strength available in a mounting joint.
Threaded inserts are available from most hardware stores and wood working stores, but our favorites come from Rampatec. We’re such big fans that we’ve partnered with them to become a US distributor for their products, with your use specifically in mind.