Flange Vented Cap For M12 Screws, ID 11.2mm x Flange Diameter 24mm, 25mm Long, Silicone (Red), Pack of 10, HLCS12-2-P
SGD $24.80
Vented caps have a ribbed internal structure to make attachment easy onto axles. Also has an exhaust port that can be utilized with simple drilling. Externally, the step design makes it easy to remove.