Subaru 2009 IMPREZA Service Manual page 2595

BRAKE
C: INSPECTION
Measure the lining thickness. If it exceeds the ser-
vice limit, replace the brake shoe with a new part.
Lining thickness
Standard value 4.5 mm (0.177 in)
Limit: 1.5 mm (0.059 in)
Rear Drum Brake Shoe
BR-28