You must put these in lights (natural or artificial) to charge the glow, if they sit in a dark garage they will not glow. You must charge these to see the glow!! 
Please note that these do not have a heavy glow.
These will break off if you only apply pressure on the duck when putting them on and off. Gently take them on and off BY THE TIRE CAP itself, not the embellishment.
Not recommended for car wash
Tire valve caps: MADE FROM BRASS, rubber o-ring gasket to prevent leakage. Universal fit 11x10mm
Great for cars, trucks, motorcycles, bikes, golf carts, etc.
I do not make the tire caps, I simply attach them together buyer assumes all risk.