F Murtz fired this volley in news:nCDcr.5107$%E2.2338
@viwinnwfe01.internal.bigpond.com:

Why are aircraft drills sometimes sharpened with a step at the end? is
it for drilling sheet in two stages?

Those are specifically for sheet metal. The so-called "bullet point"
drills you can buy now are an offshoot of that.

It's almost impossible to get a large bit to center and _stay_ centered in
very thin stock.

LLoyd