Tiny OpenSCAD module to print off a washer of any size. Just open up the .scad file and adjust the module parameters to suit your need.

// inner radius
inner = 6;

// outer radius
outer = 100;

// thickness
thickness = 2;

module washer (inner, outer, thickness) {

difference() {  
    cylinder(d=outer, h=thickness, $fn=60);  
    translate([0,0,-thickness])  
    cylinder(d=inner, h=thickness*3, $fn=60);  
};  

}

// dimensions in mm
washer (inner, outer, thickness);