Hello 1095487,

It's a little involved taking the 018999 coupling off. You'll have to tear the machine down until you can get to the bottom of the armature. It should have a slot that you can place screw driver in. The coupling is a threaded on the spindle RH. After you remove the old coupling you can thread the new coupling on hand tight. Because the way it rotates, when operating it is self tightening.

Hope this helps,
-WJA