Quote Originally Posted by curious aardvark View Post
easy. take some 3mm filament, and hollow out a 1.75mm space in the centre, then push your 1.75mm in the hole and print :-)

Other than that, dissemble the pen and fettle the gears a bit closer together.

Or simply buy a cheap 1.75mm pen :-)
the trouble is big with the gears the 3d pens are really cheap