Product review (5 stars): They are ALL made of plastic...but that's ok...
Ordered the $28.00 knob from Top Parts. Yes, it's plastic; the OE knobs from Samsung are exactly the same thing but had a metal plate on the back that made them feel heavy...total scam. Samsung should replace all the original knobs but that ain't gonna happen. So, you gotta pay 28 bucks for a plastic knob that probably cost a dollar to make. Not the suppliers fault. The bottom line is you need to replace those cracked OE knobs. Just firmly slide the new ones all the way to the stop (you'll hear it click),  and they will fit tight and look great. You just gotta pay the price and move on...