Head configurations are kinda sorta personal preference and there are differences in how they install but I agree with donn0128, use Phillips. Having said that I also have a lance and most of what I have found are #8s ranging from about 1" to 1 1/2". I have some outside covers(i.e. Reefer) that are in the 2" range and some inside Louver covers that are in the 1/2" range. Not measuring, this is my best guess. I would suggest getting a supply between 1/2 and 2. Unless you want to replace them all just go to the local hardware store and get a handfull of each.