MADE IN USA. The battery extension tube allows the use of two '18650' Li-ion batteries with the Survival Laser S4 hosts for higher battery capacity, longer total run times and at full output power. This tube can also be used in other Aurora C6-style builds that normally use two CR123A or RCR123A batteries. However, DO NOT use this battery extension tube with builds that include a 'boost' driver circuit that is limited to a maximum input voltage of 5.5-6V, as you will likely damage or destroy the driver. Also, not for use with the Survival Laser R or any of our tactical flashlights. Black anodized aluminum with bare threads for good electrical conductivity. Note: Host and batteries not included.