12BB.eu Extension for Universal Wheel Set for the belly boat
Extension tube of D=32mm (male with ball retention/female) with a length of 60cm. 
For the extension of the axle from 120 to 180cm, between the wheels. 

The extension is also easy to make to measure. Sawing to the desired length
and 1 (9mm) hole drilling for the securing (size to take over from the sawn off part).