Shoulder Screw or Idler Post
5mm or 6mm shaft should screw known as idler post
Except IPP-6_16 is mould steel, all other should screw is made of 304 stainless steel (SUS304)
5mm shaft should screw with M4 screw and 6mm shoulder screw with M5 screw
It was proved that the idler post works better with ball bearing equipped idler pulley or roller bearing and it's Press Fit. You may need tools to fix it.
Applications, CoreXY 3D Printer Prototype Use.