Different types of knock-out plugs are used when reaming holes. Which type is not generally used?

• A. Brass
• B. Aluminum
• C. Flat low carbon steel
• D. Stainless steel

Answer: (C)

Choosing the right plug material for reaming holes is about withstanding downhole conditions and not contaminating the environment. You want something that resists corrosion and wear while being easy to drive in and remove. Brass, aluminum, and stainless steel all fit these needs: they are corrosion resistant in groundwater and drilling fluids, withstand the impact and wear of field use, and won’t shed troublesome debris into the hole. Flat low carbon steel, on the other hand, is prone to rust in wet downhole environments, can deform or gall under pounding, and may shed iron oxide or debris that could contaminate the hole or interfere with the reamer. Its heavier, less durable, and less corrosion-resistant nature makes it not generally used for knock-out plugs in this context.