Just had a look at an old picky of mine lathe long gone, theres a shear pin approx. 3/16" on both lead screw and counter shaft covered over and slides away towards tailstock when they break. Had to do mine once after putting a cut on, 1ph 240v 1 1/2hp original motor barely grumbled.
No fibre gears all steel throughout, had full set of change wheels as well impossible to acquire.