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I know. My hobbed bolt is one of few other things I exploited from previous printers. The design is called Hyena and is quite expensive. I bought it on RepRapWorld few years ago.

But the one you are referring to should be just fine. The only thing that is important is that the hobbing have to make a slight groove. This will prevent the bolt from sliding out of the extruder as it do not have any nut on the other side.
The distance from centre of hobbing to inner side of the hexagonal head should be roughly 21-23mm. Either you will use the head of the hobbed bolt or you cut the hexagonal head off and place nylock hex nut or two hexagonal flat nuts on the threaded side.

Or If you don't want to cut anything, please measure the distance between centre of hobbing to the inner side of the head and I will upload another gear that will use the head without any other adjustments. That is probably the best solution, unfortunately as they are not providing any datasheet I cannot do it right away.

Edit: zhangzq71 provided 3 most common hobbed bolt spacings from centre of the groove to inner side of hexagonal head. They are 23, 26 and 30 mm. New extruder gears are uploaded to ToyREP files, so there is no need to cut anything.