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Single Plug Box of 12 Plugs
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Aviation Spark Plug With the most automated manufacturing processes and the most innovative spark plug in the aviation industry. Made in USA.

High Conductivity Copper Core Center Electrode copper, co-extruded inside a nickel alloy sleeve ensures outstanding heat and electrical conductivity while the nickel sleeve offers high resistance to corrosive combustion gases.

High Alumina Ceramic Insulator high mechanical strength, superior dielectric properties, proprietary protective glaze, provides high performance to conquer severe operational conditions. "Clean Collar" massive electrode "V" tip focuses heat to reduce fouling and enhance heat range control.

Proprietary Glass Center Seal 21st century 'fired in' resistor replaces the multipart screw, spring, carbon pile stack up used in competitive plugs and known to suffer from resistance value instability that can cause misfires, wasted fuel, engine roughness.

Nickel Finish environmentally preferable electrolytic nickel provides outstanding durable finish, superior corrosion protection, and extreme wear resistance.

Nickel Ground Electrodes aviation grade nickel electrode design focuses on minimizing sparking voltage requirements while maintaining specification gaps to ensure large, stable 'flame kernels' for on-time ignition and complete combustion.

Vacuum Infused Center Electrode proprietary, vacuum infusion process seals electrode/insulator gap providing stable heat range and superior center electrode cooling (heat flow to the insulator).

Hot-Lock Assembly intense pressure and heat create positive, zero-leakage, shrunk in seal between insulator and shell to contain the hot, high pressure combustion cycle gases.

Harness Wire Contact smooth, uninterrupted, oxide treated spring contact surface offers enhanced corrosion resistance, is chemically bonded to the fired-in resistor providing the ultimate harness/spark plug termination integrity and energy transfer.

Application Guide

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I previously installed these in the lower plugs in an IO-540 engine to eliminate lead fouling. When the standard plugs in the tops needed replacing I upgraded to the Tempest fine wire plugs. The engine now runs noticeably smoother and the mag drops are minimal. I also noticed a drop in EGTs during takeoff. I recommend these spark plugs.

Free S Verified Purchase


September 16, 2021

product performed as expected

Ed T Verified Purchase


September 14, 2021

Gerald S Verified Purchase


September 7, 2021

I bought the fine wire spark plug. To put in the bottom of my cylinder 3. Although the compression still reads 71 it seems to pump oil on that bottom plug. I have only put 4 hours on it so far. But performance seems to be the same as the massive one. I change oil and rotate plugs every 25 hours. I’ll let you know.

Jay B Verified Purchase


July 11, 2021

I have purchased these before and really like them!

Edwin G Verified Purchase


June 16, 2021

I have purchased these before and really like them!

Edwin G Verified Purchase


June 16, 2021

Yes, these plugs are expensive but hey live up to the hype! I had massive plugs that were always fouling in the bottom position of a couple cylinders. The engine was never smooth because of this. Now with the fine wire plugs the engine purrs. Just wish they were not so expensive

Eaa C
May 11, 2021

They may be spendy, but they last a long time and I have never had one foul. The set that these are replacing lasted for just under 1,100 hours.

Steve R
April 21, 2021

Very pleased with communication with staff and speed of process and delivery Purchased items packed well and received in excellent condition.

Stan O
March 15, 2021

I replaced the bottom four plugs in my Lycoming O-360 and they were an immediate improvement over the older massive electrode plugs. The engine started easier, and there was no detectable fouling which was a frequent problem in the past after engine start. Its a hefty investment, so Ill wait to replace the top plugs, but worth it so far.

Red B
September 28, 2020


Please note, Aircraft Spruce's personnel are not certified aircraft mechanics and can only provide general support and ideas, which should not be relied upon or implemented in lieu of consulting an A&P or other qualified technician. Aircraft Spruce assumes no responsibility or liability for any issue or problem which may arise from any repair, modification or other work done from this knowledge base. Any product eligibility information provided here is based on general application guides and we recommend always referring to your specific aircraft parts manual, the parts manufacturer or consulting with a qualified mechanic.

Q: Which spark plug socket will work with this longer spark plug?

Per our tech: The ATS socket should work fine, part number 12-01693. This is a pretty common size spark plug for aviation engines.

Q: When I add UREM38S to my shopping cart it changes the plug # to UREM38S XL. What does the XL stand for and is the plug longer than the massive plug # UREM38E?

No, XL just denotes that it is an iridium fine wire plug. It is not any longer than the UREM38E and will not rub on your cowling.

Q: Application chart shows 5/8 and 3/4 thread - ordering info for UREM38S doesnt seem to indicate which is shipped. When ordered which plug thread is shipped?

UREM38S is a 5/8"-24 plug. If you order UREM38S, you will get a 5/8"-24 plug.

Q: What size of gasket is used for this Tempest plug UREM38S?

This plug comes with an 18mm copper gasket.

Q: If I change to fine wire plug, do I need to change harness?

No, the harness does not need to be changed when switching to fine wire plugs. If your regular plug is an UREM38E for example, you can make the direct switch to UREM38S.

Q: Can I mix fine wire and massive plugs in an engine? Massive on top fine wire on bottom?

Yes, you can do this. People typically run the fine wires on the bottom if they are having fouling issues.

Q: What gap are these plugs pre-set to?

They are gapped .017"-.021".

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