Originally Posted by captain E34
Please put in ur too cents!!!
That thread is something like M48x1.5 and was most likely cut on a lathe before the tube was welded to the spindle. The only way for you to extend the thread would be to buy a die and do it by hand. If I had to guess, I'd say an M48x1.5 die would cost somewhere in the range of $300-$500 and for that money you can buy a conversion kit.