Removing rust is not always about dipping parts into a rust removing solution. There are times when a little elbow grease is all that is needed. These blocks made by Klingspor solve those situations when you have a smaller amount of rust to remove. The Sandflex blocks work just like the erasers we all grew up with. Just rub the block on the rust it will be erased. An abrasive material is contained within the rubber-like block to remove the rust. Like any abrasive, Sandflex removes metal and rust alike. However, the design allows it to tackle the rust more aggressively. The soft block is able to dig into crevices that hide the rust easier than other abrasives like sandpaper. Sandflex blocks work great when there is light rusting or spots of rust forming on your item. When I soak a part or use a "spray-on" rust remover, sometimes I notice a few specks of rust remaining. Removing the small areas of rust that remain is a great job for Sandflex. These blocks will last for years of rust removal. Do not confuse these with the standard sanding blocks you can buy in the store. These have abrasive material through the whole block. As the block wears, new abrasive material is uncovered.