Approximately 6mm TierraCast® gunmetal heishi beads. 1.7mm thick. TierraCast uses "Britannia" casting alloy for cast pewter components. Pronounced "hee-shee", this shape is also known as a wafer, wheel or spacer. Black gunmetal color may range from gun blue to matte dark gray to shiny black metal. TierraCast Safety Compliance Info.