If you're dabbing with a domeless nail, a carb cap is an invaluable dab tool to have as this simple looking widget is pretty effective at restricting airflow to your water pipe. Why restrict air flow you ask? For better temperature control of course and inevitably better flavor of course. With a carb cap placed over your nail, airflow becomes a lot more restricted, increasing the flavor output of each hit. Introduction of cold air is also lessened meaning that the nail retains heat for a lot longer and you won't have to resort to high temperatures (and potentially destroy some of those flavorful terpenes) to get a satisfying hit.