We've said many times that we're never going to wake up one day and invent the last SeaSucker product. That's true because our vacuum cups lend themselves to an almost infinite number of uses. The bottom line is, if you need to attach something to a rigid, non-porous surface without drilling any holes, this is the best way to do it. To make it easier for you to turn our SeaSucker into your solution, we put two slotted holes in the top (for bolting whatever it is you're mounting on there) plus a threaded (1/4-20) stainless insert. The 4.5” SeaSucker vacuum cup is rated to pull up to 120 pounds. Diameter is approximately 4.5”, but spreads out to almost 4.75 when attached. All metal parts are high grade stainless steel, even the springs inside our pump, for extra durability in the elements. Protective cap included.