Starrett GS 13. Black Granite Gage Block Stone
The Starrett-Webber gage block stones, when used moderately, may be rubbed directly on the gaging surfaces without danger of decreasing the size of the gage block. Available in 3 styles/ materials as listed.
GS 13 is recommended for use with steel gage blocks
SAO 13 is recommended for general use. Steel, ceramic, or carbide blocks
SAO 23 is recommended for use with carbide and ceramic gage blocks