Richard J Lone Tree , CO January 31, 2015 Appliance: Whirlpool Electric Cooktop RC8600XBB6 Whirlpool Cooktop Rc8600xbb6: Cooktop control knobs were worn. How to replace Knob, Control (Black). I decided to go with Appliance Parts Pros because my local supplier could only get three of the four knobs I needed. I was able to find the part easily on APP's website and then cross check it to make sure it was right. I ordered on a Monday evening and the parts showed up at our house Thursday morning-great service. I just pulled off the old knobs and installed the new ones. I'm afraid my local guy just lost a customer. Do-It-Yourself Rating: Repair Time Estimate: Less than 15 minutes