Carb cap
From Wiki Weed
A specially-crafted implement (normally made of titanium, but sometimes quartz or ceramic) which fits over a domeless nail. The purpose of a carb cap is to allow a full hit while keeping the nail at a lower temperature, which makes for a more flavorful dab. Terpenes, the flavor compounds in cannabis, are quickly degraded and changed by heat, so using a carb cap to “stoke” the oil allows the hit to still vaporize, but retains the maximum amount of flavor.
