I have a lower without a stock that I want to put an Ace Skeleton Stock on. I have to order all the parts, including the receiver extention and buffer for (I'm going to use a Wolff extra power action spring which I already have.

My question is, do I need a butt spacer to go on the end of the receiver extention to use the ACE Skeleton Stock, or does the butt of the skeleton stock screw directly into the receiver extention?

You do not need a spacer - it screws directly onto the Receiver Extension.

Cool. Thanks!