I use ABS for this, and to fit it in, I use a 5/16 to enlarge a bit of the middle hole.
Don't worry about smoothing it as it will need and grooves itself once you put it on.
It may be tight fit, so a little sanding on sides to will help to snap in, then I use machining Oil on top.

After of 20-30 big print outs, you will see that it will need to replace a new one, so print out more if you like for back up. Always inspect the the anti Z wobble after a long period of use.

You may notice, there is 2 holes for screws, your choice but no need as it will be tight fit anyway.

Hope this will help and give other different machines an idea that there is no need to use a NUT to hold on the Z.

The great thing about this is, it did not reduce of the Z height.

Got the idea from
http://www.thingiverse.com/thing:85707

No

No

.2mm - .3mm

90 - 100

Wall - 4
Bottom - 3
Top - 3