I was hoping someone could tell me what the inside diameter of their WR450 exhaust pipe outlet is. I want to be able to use a Pro Moto Billet silent insert on a yz450 stock pipe and PMB tells me it won't work. Well the young girl who answered and sounded like she wasn't exactly an expert on the subject told me it wouldn't work. So if it won't work on the stock yz pipe I thought I might be able to make my own nozzle from SS pipe and tig it to my stock end cap. I want to avoid buying the PMB endcap. $119 is kinda steep and I don't really need the spark arrestor.