Added an M5 washer at the top to first seat the nut before removing the first of two pulleys. Printed in PLA with 8 perimeters and no part cooling. Check screw and shaft alignment carefully, it might be a good idea to have something a little smaller than 5 mm to put between the screw and the top of the motor shaft. A large enough wrench to grip the whole thing while turning your 4 mm hex driver is useful. That same wrench plus a loose pulley can be useful to fully insert the pulley into the tool when clearance between the pulley and stepper is limited.
Added an M5 washer at the top to first seat the nut before removing the first of two pulleys. Printed in PLA with 8 perimeters and no part cooling. Check screw and shaft alignment carefully, it might be a good idea to have something a little smaller than 5 mm to put between the screw and the top of the motor shaft. A large enough wrench to grip the whole thing while turning your 4 mm hex driver is useful. That same wrench plus a loose pulley can be useful to fully insert the pulley into the tool when clearance between the pulley and stepper is limited.