Briggs & Stratton 2171252SM Fuel Tank Gas Gauge Cap

What It Is

This is an OEM replacement fuel cap with an integrated gas gauge for Briggs & Stratton engines, designed to let you check fuel level at a glance without opening the tank. It’s a direct fit for many walk-behind mowers, tractors, and small engines that use a standard 2-inch (50 mm) threaded fuel neck.

Fitment & Compatibility

Before buying, confirm three things:

• Thread size & neck diameter: This cap fits tanks with a 2-inch (50 mm) threaded opening. Measure your current cap’s outer diameter and thread pitch—most Briggs caps use a coarse thread, but some aftermarket tanks vary.
• Engine model & mower brand: Works with most Briggs & Stratton engines (series 450e, 500e, 550e, 625e, 725ex, etc.) and many Craftsman, Murray, Snapper, Toro, and Troy-Bilt mowers. Check your engine’s model number (stamped on the valve cover or shroud) and cross-reference with Briggs’ online parts lookup.
• OEM vs. aftermarket: This is an OEM Briggs part (2171252SM). It’s a direct replacement for the original cap. Aftermarket caps may fit but often lack the same seal quality or gauge accuracy.

Key Things to Know

• Installation is tool-free: Simply twist off the old cap and screw on the new one. Hand-tighten only—overtightening can crack the plastic housing or damage the gasket.
• Gauge accuracy varies: The float-style gauge gives a rough estimate, not a precise measurement. It’s most accurate when the mower is on level ground and the engine is off.
• Seal quality matters: The included rubber gasket creates a vapor-tight seal. If your old cap leaked fuel or fumes, replace the gasket (often sold separately) if it’s worn.
• Common gotcha: Some aftermarket or replacement tanks have a deeper neck that can prevent the gauge float from reaching the bottom—test fit before final assembly.

Should You Buy It

Buy this if you want a simple, drop-in OEM replacement that adds fuel-level visibility without modifying your tank. It’s especially useful for mowers with opaque plastic tanks where you can’t see the fuel level otherwise. Avoid if you need a locking cap or if your tank uses a non-standard thread size (e.g., 1.5-inch or metric).