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Gluing in a patch didn't work perfectly for me. I made my bench from construction lumber, doug fir 2X4s. I mortised in 2" square patches of hard maple where I put my holdfast holes, about 1/2" deep. The maple might have kept them from going oval for a while, but three years later the maple has split in my favorite holes and the holdfast doesn't grip as well. I think that the 2x2x0.5 inch patch was too small and that it didn't get enough support from the fir underneath. A larger piece of home-made plywood from maple or maybe some hickory might have worked better. I have a single LN cast holdfast. I do rough the contact points up with 60 grit sandpaper occasionally which does help the grip, but also turns my hands black. I also started pounding it in with a 4 lb iron hammer and haven't split my jointers mallet since.