HKS 50003-M50HL Super Fire Racing M-Series Iridium Spark Plug HL Type HR 50

Vehicle Fitment

• Universal Fit - Multiple Applications (HL Type, 12mm x 26.5mm Thread, 14mm Hex)

Fitment Notes

• Universal part - no vehicle-specific fitment assignment applies
• "HL" suffix denotes a 12mm x 26.5mm thread with a 14mm wrench hex - distinct from the XL Type (16mm hex) despite sharing the same thread diameter and reach; confirm hex size before ordering
• Heat range (HKS #50 / NGK #10) is two steps colder than Nissan GT-R R35 stock (NGK #8) and one step colder than Toyota 86 / Subaru BRZ stock (NGK #9) - intended for high-tuning applications
• Sold individually (1x per listing) - order quantity to match your engine's cylinder count

Features

• HL Type format with 12mm x 26.5mm thread and 14mm hex - the first M12 long reach HEX14 plug released by HKS
• 0.6mm iridium alloy center electrode centered within the plug body for wider combustion coverage and improved flame propagation
• Enlarged outer electrode design reinforces durability and supports stable ignition at high load and high RPM
• Square platinum chip on outer electrode boosts ignition efficiency and long-term wear resistance
• Thermal edge insulator design actively discharges to reduce carbon deposits on tuned engines
• Spark support gap provides a secondary discharge zone to maintain ignition reliability under fouled conditions
• Nickel-coated housing resists corrosion and protects against premature housing deterioration
• Engineered specifically for heavily tuned engines requiring a colder heat range beyond NGK #9

Specifications

• Part Number: 50003-M50HL
• Series: Super Fire Racing M-Series
• Type: HL Type
• Center Electrode: 0.6mm Iridium Alloy
• Outer Electrode: Square Platinum Chip (Enlarged)
• Thread Size: 12mm x 26.5mm
• Wrench Size: 14mm
• Heat Range (HKS): 50
• Heat Range Equivalent (NGK): #10
• Heat Range Equivalent (Denso): 31

Included Components

• 1x HKS Super Fire Racing M50HL Spark Plug

Product Description

The HKS Super Fire Racing M50HL is a purpose-built, high-heat-range iridium spark plug designed for heavily modified engines that push beyond the thermal limits of NGK #9-range plugs. It was the first plug HKS released in the M12 long reach HEX14 format, developed primarily around the Nissan GT-R R35 (VR38DETT) and Toyota 86 / Subaru BRZ platforms, where aggressive tuning demands a significantly colder plug than OEM spec. At NGK #10 equivalent, the M50HL runs two steps colder than GT-R R35 stock and one step colder than 86/BRZ stock - making it the correct choice for high-boost, high-compression, or race-spec builds where heat management is critical.

Unlike standard M-Series plugs, the M50HL features an enlarged outer electrode for added durability and a centered iridium tip geometry that improves flame propagation across the combustion chamber. The thermal edge and spark support gap work together to resist carbon fouling that commonly affects tuned engines during varied load cycles. Always confirm the 12mm x 26.5mm thread and 14mm wrench hex match your application - do not confuse with the XL Type (16mm hex) before ordering. Sold individually.