When the electron is shot out of the muzzle of an electron gun it emerges with a particular velocity and travels along a well defined trajectory. The electron carries a precise charge of 1.6*10^-19 coulombs. By careful design, an electron gun can make the electrons spin - like the rifling inside the barrel of a gun can make bullets spin.

All attempts to measure the radius of the electron have failed! All we know is that the radius is less than 10^-18 m; that is, its radius is one hundred million times smaller than that of the atom. All the known properties of the electron are consistent with the assumption that its radius is zero. As far as we know, the electron has no structure.

What is puzzling is how a particle can have no size and no structure and yet can have a definite mass and behave as though it is spinning? We do not know the answers to these questions but scientists are working on experiments to find out.

Information provided by: http://www.iop.org/Physics