measured 19mm, checked with scad which also says 19mm
from x-end.scad
// Screw holes for TR nut
%translate(v=[0,-17, 0]) rotate([0, 0, -135]) translate([0, 9.5, -4]) cylinder(h = 19, r = 1.65, $fn=50);
%translate(v=[0,-17, 0]) rotate([0, 0, -135]) translate([0, -9.5, -4]) cylinder(h = 19, r = 1.65, $fn=50);
ie -9.5 to 9.5 19mm.