Drill rod Mikado... A large part of the rods that we were using appeared to be so rusted on the inside that the inner tube became stuck on its way up and down. This resulted in numerous wireline cable breaks (the fact that the cable had been rusting somewhere outside for the last 10 years did not help here) and once we drilled without the inner tube assembly in place. This means that you drill the core but that it does not go into the core tube but rumbles around in the corebarrel instead. Eventually, after replacing all the rusted rods, we succeeded in retreiving 8 of the 10 feet of this core.