The Original Convert-A-Ball® system has three industry standard sized towing balls 1-7/8", 2" and 2-5/16". Each ball has a patented NON-REMOVABLE pin that with a push of a finger or regular screwdriver comes out of the shank and pops right off, but is 100% totally secure while towing! With the trailer coupler on the ball and shank there is no where for the pin to go and disengage from the shank. It cannot unlocked or untwist. When you are not towing, you will never lose then pin because it is designed NOT to fall out of the ball itself.