You should use whatever came with the kit. Otherwise, its difficult to say without knowing which arms you have bought and whether or not they have castor built into them already or not. Depending on whihc arms you have, some of the arms out there are stock arms that have been lengthened, if thats what you have then you need to use whatever is normal for a 3.5" lift, I believe. I think you are confused b/c of the other member on here who is having problems with his particular vehicle. Unfortunately, it appears somethign is uniquely wrong with his particular job (either the arms set or the axle); lots and lots of folks have installed the long arms (from various vendors without these complications). So, if you can provide more info, then you will get more info, without knowing what you are working with, its difficult to say anything. You could always call whoever you bought the arms from and ask what they would recommend. HTH