3M 28403 Instruction Manual page 8

Type 27 Grinding Wheels are also known as Depressed Center Grinding Wheels. They have a dish shaped center to allow the lower mounting hardware or flange
to be recessed into the wheel. This allows the wheel to be used in a nearly flat orientation when needed.
Model 28403 has a 3/8"-24 spindle to be used with Type 27 Grinding Wheels with 3/8" center holes (CH).
Model 28405 has a 5/8"-11 spindle and can use wheels with either 16 mm or 7/8" center holes (CH).
Model 28403 can accommodate an adapter to change the spindle to 5/8"-11 spindle to allow the use of wheels with either 16 mm or 7/8" center holes (CH).
Refer to ANSI B7.1-2000 Safety Requirements for Use, Care and Protection of Abrasive Wheels and ISO/EN 12413 Safety Requirements for Bonded Abrasive
Products for proper abrasive wheel applications.
MOUNTING 3/8" CENTER HOLE TYPE 27 WHEELS
Lower Flange for 3/8" CH
Type 27 Wheels
Figure 1
Type 27 Wheel with 3/8"
Center Hole, properly
mated to Upper Flange
Figure 3a
Type 27 Wheel Mounting Hardware and Usage
Upper Flange for 3/8" CH
Type 27 Wheels
Lower Flange: NOTE:
Curved surface goes into
the wheel's center
Figure 2
Lower Flange for 3/8" CH
Type 27 Wheel properly
mounted
Figure 3b
8
Upper Flange:
NOTE: Wheel's curved backside
goes into the flange's center