Spi 91-404-4 Feeler Gauge Parallel Leaf 0.40mm

Product Description

The SPI 91-404-4 is a single parallel-leaf feeler gauge used to measure precise gap clearances in mechanical assemblies and engine components. The leaf measures 0.40 mm in thickness, 0.5 inches wide, and 12 inches long, providing a consistent flat contact surface across the full length of the blade. Constructed from high carbon steel, the leaf resists wear and maintains dimensional accuracy through repeated use. Machinists, diesel technicians, HVAC service techs, and engine builders rely on this type of feeler gauge for valve clearance checks, bearing fit verification, and alignment measurements.

This feeler gauge is suited for use in both shop and field environments where a single specific thickness blade is needed without carrying a full set. The 12-inch leaf length accommodates wider assemblies and allows reach into restricted areas. The parallel leaf style ensures uniform thickness from tip to base, which is critical for accurate gap readings. Common applications include checking spark plug gaps, valve lash, breaker point clearance, and machined surface fit in automotive, HVAC, and general mechanical service work.

Key Features

• Parallel leaf style provides uniform thickness across the full 12-inch length
• 0.40 mm blade thickness for precise gap measurement
• High carbon steel construction for durability and dimensional stability
• 0.5-inch blade width for stable contact on both narrow and wide gap surfaces
• Single-leaf format for targeted use without a full gauge set

Compatibility

Designed as a general-purpose feeler gauge blade for use in automotive, mechanical, and HVAC service applications requiring a 0.40 mm gap measurement.

Installation Notes

Insert the gauge blade into the gap with light, consistent hand pressure — the blade should slide with minimal resistance for a correct fit reading. Do not force the blade or use it as a pry tool, as this can alter the blade geometry and compromise measurement accuracy. Clean the blade before and after use to prevent contamination of precision surfaces. This tool requires no installation but should be stored flat to prevent warping.