This is an underwater noisemaker for communicating while scuba diving. I simply start the print and after the wall is formed up about an inch, I drop in a couple of 1/4 20 nuts. Anything heavy enough to shake should work, but I had these in my basement. The loop on top should attach to a small carabiner or to a key-chain Alternatively, tie some cord and attach it wherever is convenient and safe. I print it solid for strength and water-tightness.