Generally all abrasive wheels provide us with sufficient information of the different measurements or dimensions that characterize them. These dimensions are expressed in inches and / or millimeters and are printed on the identification labels of each manufacturer; or in some cases this information may be printed on the body or face of the disc as in metal discs for cutting wood, ceramics, marble, concrete, among others.
Basically the information that is offered to us is:
Diameter of the disc.
Diameter of the power shaft or coupling of the tool with the wheel.
Take as an example the dimensions described in image 1:

Image 1. Dimensions of the wheel in inches.

Diameter of the disc: 4½ “(Four and a half inches).
Thickness: 3/64 “(Three sixty-four-fourths of an inch).
Shaft diameter: 7/8 “(Seven eighths of an inch).
On the other side, image 2 shows the dimensions expressed in millimeters:

Image 2. Dimensions of the wheel in inches.

Diameter of the disc: 115 mm.
Thickness: 1.2 mm.
Diameter of the axis: 22.23 mm.
When buying or acquiring an abrasive wheel always keep in mind the dimensions of it, and especially those of the shaft of the tool since not all are equal and this could represent a considerable expense or loss of money.