Andy
Eurekastar is right, a Kirby HEPA bag would not fit, as the hole is slightly larger than the one on the Hoover A bag. If you wanted to use a Hoover A HEPA bag but concerned about the cost per bag or the hassle of special ordering the bags thru your local shop, there is an alternative....just use a generic Hoover Y HEPA bag. Most vac shops should carry them & they are easily found on Amazon.com for dirt cheap when bought in bulk. Also, it says in your profile your Hoover is a Hoover Tempo, right? The Type A HEPA bag, as well as the Kirby bag would be too big & not inflate properly, & the Tempo does use the Y bag anyways.
If you had another Hoover, though, & for some reason you still want to use the Kirby HEPA bags, there is a way to do it. With my Royal uprights that use the Royal Type B bag, I wrapped duct tape around the filltube to increase it's diameter, so that a Kirby bag fits snugly without coming off. You could do the same with your Hoover if you wanted to use a Kirby bag.
Hope this helps....Rob