The nice one board top has a check on one end that went more than half way across the top. It had been "repaired" by nailing small finishing nails into the edge. Although this will hold the edge together it does not correct the problem. It must be glued to stop its spread and strengthen the top. To repair this fine, tight crack we first tape the top finished side to not allow any glue to escape. Then clamp a "batten board" across the top to insure it is flat at the joint. The most appropriate type of glue to use on this kind of repair is a thin cyanoacrylate. It will penetrate the tightest of cracks and into the wood fiber. Just keep adding until the crack is completely filled.