This is a very cool idea -- wish I'd thought of it!
This little device is the cure to dreaded "spouse comments about holes in carpet" as well as dirty looks when you spike your bass into somebody's wooden floor. It also will help avoid having your endpin skid across smooth surfaces.
This semi-hard solid rubber ball may outlast either of us! It is made so your endpin goes up to one inch into the ball, depending on the sharpness of the tip. It is designed to handle the tip or blunt end. It's simple -- you dial the small screws to size it to your endpin, and then use the larger knob to tighten it. The sleeve is just large enough for the popular 10mm endpin shaft size, and easily dialed down to the 8mm size, or other sizes smaller than 10mm. For the metric-impaired, 10mm is .39 inches (25/64th), a bit larger than 3/8".
This will not fit ALL bass endpins. Will it fit yours?
The endpin ball will fit an maximum endpin diameter of 10mm, which is around 3/8". If your endpin is larger than 10mm or 3/8", do not buy the endpin ball, it will not work with your endpin. Size matters!
Do you need an easy way to determine if your endpin diameter is too large? Here's what you do: grab a 10mm open-ended wrench out of your toolbox (the size is stamped on the side of the wrench). If the wrench can straddle the post (even if it's touching) then congratulations, the endpin ball should fit your endpin! See the last product photo above for a visual description of the endpin ball's dimensions, to ensure fitment. Also note that if your endpin has a "collar" near the point, you should also check the details in that photo to make sure that it won't interfere.
To save you some time, this will not fit the stock (bare steel) Kay/Engelhardt endpin, which is 1/2".
While this endpin ball is robust, nothing is permanent, and, depending on use, it will eventually need to be replaced if significantly worn.