How rare is this? I bought 3 Ushio 400w 14K bulbs to put in a Giesemann Spectra, only one bulb fit. The other two had wider and shallower threads couldn't even get them started. How is it that a manufacturer have different threads on their bulbs. I thought all MH bulbs would fit all MH lights. I mean this is crazy, isn't there some kind of industry standard?