There are a few factors to consider when deciding whether to use needle nose pliers or locking pliers to screw on broadheads. The first is the size of the broadhead. If the broadhead is too large for the needle nose pliers, then you will need to use locking pliers. The second factor is the type of material the broadhead is made from. If the broadhead is made from a softer metal, then you can probably get away with using needle nose pliers. However, if it is made from a harder metal, then you will need to use locking pliers so that you don't damage the head. Finally, you need to consider how much force you will need to apply in order to get the head screwed on tight enough. If you think you will need a lot of force, then it is probably best to go with locking pliers so that they don't slip and cause injury.