Rubber Bung Plug with Breather Hole 14-20mm comes with straw

Upper Diameter 20mm
Lower Diameter 14mm

This is a drain plug that you remove to allow water to drain from inside the hull of your kayak or boat to the outside. You may not need to do this typically before you put the boat away .but most kayaks and dinghies have a hole to allow this to happen.

This plug is not for scuppers (when removed these let water off the top of your deck or cockpit into the water- these are typically a lot larger.

Suits particularly SSLSA or downwind Composite skis that benefit from or need a breather Tube as well as some sailing dinghies (Laser dinghy etc)

Comes with heavy duty breather straw/tube
The purpose of the tube is to reduce water ingress (getting into the inside of the boat or kayak) and still let air in and out to help avoid damaging the craft.
Taking your craft kayak from a hot environment (roof of car in summer for example) into a cold one (the water) will cause the air on the inside of your boat to contract and vice versa. If there is no breather this can cause damage. In the worst case change the shape or damage the hull or deck, or more commonly cause the bung plug to pop out (or get jammed into position). Having a breather hole means you can leave the bung in the hole except when actively emptying your craft reducing the risk of losing it.

Note this plug is not threaded it’s held in by friction (you jam it in) – some craft use threaded bungs (e.g. Bic skiff, Finn Kayaks, and most spirit kayaks etc.) These are also available.

Other rubber plugs are available and in a range of sizes but without breather tubes/hole.