There are more than one type of base on single ended bulbs. The only one I know is Mogul base, which I have. Great price, too bad I only need 175 on my 120g. What wattage are the MH on the Hamilton you sold me? If the wattage is right I'll take the other one. Or both if Steve can't use one and if they are Mogul base. I'll call you when I get off this darn thing. Sue