This seems like a technical maintenance request from someone who likely owns a Breville machine with a built-in grinder, like the Barista Express or similar models.

Here provide clear, step-by-step instructions covering safety precautions, disassembly, cleaning, replacement, and reassembly. The user specified "44.6mm" which matches the conical burr size found in many Breville grinders.

While specific steps can vary slightly by model (e.g., Barista Express, Pro, Dual Boiler), the process for replacing the 44.6mm conical burr set (the upper and lower burrs) is generally the same for most Breville espresso machines.

Important: Before starting, unplug the machine. You will likely need a flathead screwdriver, a Phillips head screwdriver, and a 9mm or 10mm wrench (or socket).

 1. Remove the Hopper and Outer Burr

• Empty the hopper and remove it by twisting it counter-clockwise to the “Unlock” or“Remove” position.
• Locate the outer burr (the ring with the handle). Turn it counter-clockwise to lift it out.
• Note: If the new burr set came with a silver shim washer, save it. Only add it later if the machine grinds too coarsely on the finest setting.

 2. Remove the Upper Burr Carrier

• Use a flathead screwdriver to pry out the metal or plastic washer holding the rubber seal (the “wiper”) in place.
• Remove the rubber seal to expose the three Phillips head screws beneath.
• Unscrew these three screws to lift the plastic carrier off the machine.

3. Remove the Lower Burr

• The lower burr is reverse-threaded. To loosen it, turn it clockwise.
• To lock the shaft, insert a Phillips screwdriver through the hole in the center of the gearbox (where the coffee usually falls out) to act as a stabilizer.
• Use a wrench on the hex nut of the lower burr to turn it clockwise until it comes loose.

 4. Clean and Install the New Lower Burr

• Clean out all old coffee grounds from the cavity.
• Screw the new lower burr onto the shaft. Because it is reverse-threaded, tighten it by turning counter-clockwise. Tighten firmly, but do not overtighten.

5. Install the New Upper Burr Carrier

• Place the new plastic carrier onto the machine.
• Reinsert the three Phillips screws.
• Replace the rubber seal and the metal retaining washer.

 6. Install the New Outer Burr

• Insert the new outer burr (the ring) into the carrier.
• Turn it clockwise to lock it in place.

 7. Reassemble and Calibrate

• Reattach the hopper and fill it with beans.
• Run a calibration: Set the grinder to the finest setting. If the motor stalls, sounds strained, or the burrs make a “metal-on-metal” screech, stop immediately and turn it coarser.

Pro Tip: If you find that even on the finest setting (e.g., "1" or "Fine"), the espresso runs too fast, you need to add the shim washer under the outer burr. If the burrs grind too fine and choke the machine, remove the shim if one was installed.

If your machine has aremovable magnetic upper burr (common in newer models like the Barista Touch Impress), the process is simpler—you typically just lift the handle, twist the outer burr out, and click the new one in without needing tools for the disassembly.

SUS420J2 coffee grinder burr mainly depends on the usage scenario (home/commercial), grind size and maintenance level, with the following general references:

• Home use (10-30g ground daily, mostly medium-coarse grind, regular cleaning): 800-1200kg of beans can be ground in total, with a normal service life of 2-3 years.

• Light commercial / high-frequency home use (50-200g ground daily, including fine grind, standard maintenance): 300-500kg of beans can be ground in total, with a service life of 1-2 years.

• Rough use / no maintenance (frequent fine grinding, no burr cleaning, grinding hard beans/foreign objects): The grinding capacity will drop sharply to less than 100kg, and the burrs are prone to chipping and blunting.

SUS420J2 is a martensitic stainless steel with moderate hardness (HRC 50-55 after quenching). Abrasion during grinding is mainly caused by the wood fiber and a small amount of minerals in coffee beans. Fine grinding (e.g., for espresso) causes more intense burr friction, with a wear rate 2-3 times higher than that of medium-coarse grinding (e.g., for pour-over coffee).