How to mounting grinding discs ?

How to proper mounting the grinding disc to angle grinder is very important for abrasives safety and perform a good grinding works. 

a). When the adaptor has been tightened, there should be a slight clearance between the flange and the wheel . This ensures that clamping pressure is exerted only at the centre of the hub section.

b). The outer part of the face of the flange adjacent to the wheel should be tapered as above and this allows the full width of the flange to support the wheel during the grinding operation.

c). A paper washer should not be used on the hub section of a depressed-center wheel.

It's better run the angle grinder some seconds after fixed the grinding disc,  start your grinding discs carefully when everything be Ok.