water not spraying from the lower and upper arm

Ok, after reading all the posted on the impeller removal, I order one, I took my whole assembly apart I see what my problem was that cause the impeller to brake,I removed the old, now I’m have problem installing the new impeller

The shaft of the motor has thread and the new impeller suppose to screw onto the shaft
With the engineering caliper I measure the size of the thread on the motor shaft is
(.3 of inches) but the hole on the impeller is only (.2 of inches), I have tryed to force the impeller on but with no luck, can you place tell me what I’m doing wrong

should I try to re-thread the impeller with TAP to larger size,
the part number I order is WPL 819351
please help