Nice job. I've never thought about scratching a line with my tool to help line up the holes. I'll have to try that out the next time and see if it improves my success rate. Also a good point about doing it from a good stance. A couple of years ago 3 of us v threaded off a 4 pitch climb. For the last rap the first down stopped on a slabby ledge couldn't get the screws to connect, we made fun of him then each of us missed again. We repositioned on a small ledge a little higher up and hit it on the first try. Having both hands free, not semi hanging, and off the calves did the trick.