Prepare Lag Screw Supports

What happens here

Once all lag screws are securely installed and protruding from the wall, use a reciprocating saw equipped with a metal-cutting blade to carefully cut off the heads of each lag screw. Cut them as close as possible to the wall surface, ensuring a clean, flush break. This leaves the threaded shank of the lag screws exposed, acting as sturdy, fixed dowels that will be inserted into the mantle.

Goal: Cut off the heads of the installed lag screws flush with the wall to create robust, protruding metal dowels for the mantle to slide onto.