On Wed, 02 Sep 2015 14:33:10 +0100, John Rumm wrote:

The smaller helical thread is actually the output shaft of the motor
armature. Its a very common way to finish the shaft on the armature. If
you look at my recent replacement of the aramature on my Makita drill,
its a very similar design:

http://wiki.diyfaq.org.uk/images/e/e...oxArmature.jpg

So you would need to replace the armature is its the shaft that is worn.

Ah, I see that now. New armature is £26.73.