"AAvK" writes:

These are what I use.
http://www.dmtsharp.com/products/duosharp.htm

They work great and fast.
Dave


What type of stones, what are they made of?

Carbon.

--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
Phone: +49 228 73 2447 FAX ... 7869
Physikalisches Institut der Uni Bonn Nussallee 12, D-53115 Bonn, Germany
CERN: Phone: +412276 76461 Fax: ..77930 Bat. 892-R-A13 CH-1211 Geneve 23