The easiest way to tell them apart is by checking the packaging they came in. But if you don't have that handy, just take a quick look at the acoustic channel – the hole inside the earplug ring. You can spot the difference between Loop Engage™ 1 Plus and Loop Engage™ 2 Plus by the size of the nozzle: Loop Engage™ 1 Plus has a 5 mm nozzle, while Loop Engage™ 2 Plus has a 4 mm one.