Mercury - Drain Screw 25HP-40HP TwoStroke Outboards Precision Fit 8542464. Overview. Sometimes, it's the smallest parts that keep your engine running its best. The Mercury 8542464 Drain Screw is one of those unsung heroes - a simple yet essential component that helps keep your carburetor clean, tight, and properly maintained. Designed for Mercury 25HP-40HP TwoStroke outboards, this drain screw provides a perfect seal every time, ensuring smooth maintenance and preventing leaks or air intrusion i