This spark plug gap tool set is designed for accurate and consistent adjustment of spark plug electrode gaps. Proper gap ensures stable ignition, better engine performance, and improved fuel efficiency. Compatible with most 10mm, 12mm, 14mm, and 16mm spark plugs (not for 18mm). The included 32-piece feeler gauge set covers 0.0015″–0.035″ (0.04–0.88mm), suitable for most vehicles. Easy to use: insert the spark plug, adjust with the knob, then verify using the feeler gauge. Slightly reverse the knob before measuring to reduce springback error. Made of durable alloy steel with hardened, polished gauges for long-term use. Suitable for DIY maintenance or professional repair. Package includes: 1 tool + 32 feeler gauges.