If using wooden skewers, wrap ends in foil before adding to grill to prevent them from burning. Also, skewers can be soaked for about 1 hour in water before using to prevent them from burning on the grill.
Arbol chiles have a heat level of 7.5 on a scale of 1 to 10. With a Scoville heat unit between 15,000 to 30,000, they have about as much heat as ground red pepper (cayenne). Use fewer peppers if you want less heat.
Substitute 2 Tbsp. crushed red pepper for the arbol chiles.