304 Stainless Steel Unthreaded Monroe Pull Knob I purchased a medium size (PH-0251) which was perfect for the outside bottom handle on a wooden garage door. It has no sharp edges, it's thick enough for good strength, it comes with 6 decently sized stainless steel screws to hold it firmly to the wood, and the austenitic stainless steel (see below) is of a very high quality that won't rust . If not damaged, this pen should last for several lifetimes. Use another of the same (same size) on the lid (roof) of the generator shed. See customer image (on cover, front, center). Types of Stainless Steel: There are three main types of stainless steel: austenitic, ferritic and martensitic. austenitic. With austenite as the main phase, these alloys contain chromium and nickel (sometimes manganese and nitrogen) built around a composition of Type 302 iron, 18% chromium and 8% nickel. Austenitic steels are non-magnetic, are not hardened by heat treatment and are almost completely resistant to corrosion (depending on the chromium and nickel content). The most well-known stainless steel is 304, which contains 18-20% chromium and 8-10% nickel. ferritic. With ferrite as the main phase, these steels contain iron and chromium. Ferritic steel is somewhat magnetic, less ductile than austenitic steel, is not hardened by heat treating, and is rust resistant (or better, depending on chromium content). martensitic. Martensitic main phase are low carbon steels. They are magnetic, can be tempered and hardened and are only rust-resistant to a limited extent. Martensite gives steel greater hardness but reduces its toughness and makes it brittle.