I've hade some safety clips made up by D.Faulkner Springs, very pleased with the result but drilling the adapter hubs is proving very difficult, I'm using 4mm cobalt drills, I've managed 3 hubs (2 holes in each) but the 4th is proving impossible, the adapters and wheels are from Vintage Wheels US, the adapters are forged steel, any ideas anyone what drill would do the job.