3/8" to 1/2"

[PowerfulKitty]

You can also see that the shaft coming out of the gearbox is tapped (probably 1/4-20 or 10-32). You can drill and tap the same hole into a piece of your 1/2" hex shaft and then connect them with a piece of all thread (ready rod). If you have a metal lathe and someone who knows how to use it, it is quite easy. We did this to extend the shafts on our VexPro VersaPlanetary gearboxes.