Silver Probes for the Windsor Probe device measure normal-weight concrete with strengths from 3,000 to 17,000psi (20.7 to 117.2mPa). Probes are high-strength steel alloy hardened to Rockwell C48. Special low-power adapters position the probes further down the barrel for testing of concrete with strengths below 3,000psi. Probes are purchased separately in Cases of 25 Kits. Each Kit contains Three Probes and three power loads, to run one test.