When adding a letter, I may become boring;
When fused with some latex, I help with card storing.
With the help of King's clown, I become one who steals;
With false fans behind me, in boxes with wheels.
My thickness may alter your internet speeds;
With a measure of time, I stop that which bleeds.
Part of the circle that's loose on the lean;
Replacing one vowel, I'm serving the Queen.
I sound like a ruling that one is forbidden;
Also, in addition, when first letter hidden.
What am I?