I have been training grippers for a little under three months now and am happy to reach these closes. My training gripper was the Heavy Grips 150. After being able to rep it for 6 x 6 I changed strategy a bit with some advice. I started doing 6 x 3 reps and setting each rep at around 20mm (I passed the handle of another gripper through each time) and held the end of each rep for 3 seconds. I built that up to 6 x 4 holding the end of each rep for 5 seconds. That got me both of these closes.