We purchased my son a "hop ball" and somehow the plug got lost before I had a chance to blow the ball up. Here is my solution for not having the plug. I printed it in PLA. You will have to use pliers or a similar tool to grab the "shoulder" to remove the plug if you need to air it up again or if you are removing the air for storage.

No

No

0.2 mm

10% or more

Print settings are not super important just make sure you have good layer-to-layer adhesion.