This hose stopper is designed for irrigation hose with a 6mm inner diameter. Commercial stoppers for this type of hose were difficult to find locally.
It doesn't seal 100%, which was fine for my irrigation application. I suspect if sliced with "randomize starting points" it may seal better. A zip tie or hose clamp can also be added to improve sealing.
In the photograph the stopper is shown inserted in to a larger than 6mm hose for illustrative purposes.