It's been a while, but my recollection is I expanded the existing hole to 3/8 by pulling a forstner bit backwards through the hole, letting the shaft be the guide.I think i was barely touching the reinforcing crossbolt. I used lamp rod as pillars and I may have flattened one side a bit (took off a few threads with a dremel) nearest the crossbolt. In any case, it seems to have worked for me.