The boss is 50mm from top to blade. Thing is, if the boss sits against the bottom of the shaft, the length of the boss shouldn't matter, should it? The blade on the GMC is about 3mm thick steel, very heavy duty and I reckon on a standard lawn you would get many years out of it. Here is the boss off the shaft. Shaft diameter is 22mm. Looks to be about 20mm thick inside meaning it would sit on the bottom of whatever shaft it was on so height of the blade would be the same as current one.
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