Amazon.com : ALEOED 2 Pieces Bicycle Brake Pad Spacer Hydraulic Disc Brake Spreader Instert Tool Parts for Shimano and Other Mountain Road Bike MTB : Sports & Outdoors
Amazon.com : Fabbay 4 Pieces Bicycle Brake Spacer Disc Bike Hydraulic Disc Brakes Pads Bike Disk Brake Spacer Bike Brake Pads Empty Pinch Cycling Repair Tools Compatible with Shimano, MTB, Mountain Bike
What are these called? Cylindrical spacers under disc brakes.. : r/bikewrench