These Tungsten Carbide Tipped holesaws (for steel and stainless steel)  are the ideal solution to your metal cutting needs.  They can also drill through wood, plastic, steel and many  materials.

Available in 3 sizes:  20mm, 22mm and 32mm

They are sold as a full assembly so no arbour is needed.  A spring built into the holesaw pilot ejects the core after drilling

It is important to use a cutting lubricant or WD-40 while drilling.  300 RPM recomomended when drilling stainless steel.