What are Slip-on Flanges? For lower pressure applications, high-quality stainless slip-on flanges, steel slip-on flanges, and stainless steel slip-on flanges are suitable. Welding these pipes lowers their fabrication costs. These can be used in a wide range of sizes and applications. Slip-on flanges are one of the most common styles of pipe flanges. The faces of these flanges are usually elevated or flat. The flange bolt holes are aligned with the pipe, and the flange face is squared. Slip-on flanges are available in sizes ranging from 1/4″ to any size.