On Tue, 17 Jan 2012 07:14:21 -0500, dadiOH wrote:

It is a fiber circle, about 1/8" thick, with grit embedded in it. The
grit is probably corundum (aluminum oxide). They cut by grinding, wear
pretty fast and are way less than $5.00.

A 'circle' would be just perfect for the sprinkler head in this picture
to pop up inside the stone:
http://www1.picturepush.com/photo/a/...40/7364584.gif

But for most of these, I would need something straight:
http://www3.picturepush.com/photo/a/...mg/7364581.gif