It depends on the material and how "clean" your drilling is, but a 12.5 mm is 0.492126 inch.... only .008 smaller than a 1/2 inch. You could try that - it could have a little more slop, but not much.
(I don't recall if I've done it with this bit or not - I've done a couple in a pinch in the past when I had a dull bit, but that went away when I got my drill doctor).