This 24” Septic Tank Risers come in three different sizes, 3”, 6”, and 12” with a riser lid, adapter plate, and screws at no costs. Each riser is securely locked in with stainless steel screws. This product is made from High-Density Polyethylene (HDPE), one of the most durable thermoplastic polymers, compared to other Polypropylene (PP) risers.