Corner forms are designed to fit in inside corner locations, use standard forms for outside corners . The corner form installs easily by screwing into the inside corner of two splash boards. Made of resilient polypropylene . CPS forms are designed to fit on top of an 12” Sonotube. They can be reused if carefully removed or they can be merely used once and disposed of. No more building and staking forms for the pier. They save time and are simple to install with 4 screws.