Assuming that 1 is right, then 2 is right, because only one of the three statements is right, so 1 is wrong; 2 is right and 3 is wrong, so Xiao Du is a fitter and Xiao Li is not a lathe worker, so he is an electrician. 1 is also right, so 2 is wrong; That's right. Xiao Li is a lathe worker, Xiao Zhang is not a lathe worker, but a fitter, and Xiao Du is an electrician.

So, we can only be sure that 3 is right.

Xiao Zhang is a fitter, Xiao Li is a lathe worker and Xiao Du is an electrician.