These are heavy duty (high torque) plum flexible shaft couplers. They are made of hard aluminum alloy. The couplers are designed to be flexible so they can be fit to two shafts even if they are not perfectly co-linear and will help reduce binding effects. 

The way they are designedt, create a spring effect in the X Y & Z linear axis but not in the rotational axis. That means that you will not get increased backlash - so they're suitable for precision and heavy duty CNC work.

This coupler will connect a 10mm diameter shaft to an 14mm diameter shaft.  

• d1=10mm / d2= 14mm 
• Outer diameter (D): 30mm
• Length (L): 42mm
• L1= 11mm
• L2= 13mm
• L3= 5mm
• Maximum Torque: 6N.m
• Eccentricity Error: 0.2 mm
• Shaft Angle < 1 degree