I am putting new boards on an older cast iron bench. The old boards are held on with stainless steel threaded inserts and stainless steel phillips head bolts in 1/4-20 thread. Could not figure out how to remove the inserts so i split a board. There is no apparent means of inserting or removing the threaded insert. How did whoever made this bench install the inserts? The inserts are the same on each end. They could be installed either end into the wood first from what I can tell.