I used a close pipe nipple(the one that's all threads), It was 3/4" pipe. Cost less than $1 at the hardware store. Anyway, it needs to be just big enough to slide over the top of the injector after you pull the retainer off. Then take one of your lug nuts off, screw it on the top of the injector, and tighten it down. Pops them right out, no jerking, prying, or beating that could mess up your threads.
Scott