The stainless steel screw is made of AISI 304 stainless steel hex bar. AISI 316 is also good stainless steel for marine. It is customized stainless steel screw. It is cut, CNC machined, and CNC milled. After machining, the milling surface roughness is Ra 3.2, the CNC machining surface roughness is Ra 1.6. If need, Ra 0.8 or Ra 0.4 is also available when using special blade, with price increased. It is on demand.