5/8 vs 3/4 avaition spark plug connectors

[Dorfie]

Please help me understand the difference between the 5/8 and 3/4 inch wire to spark plug nuts.
Is the spark plug thread size into the cylinder head unaffected by the two different sizes?
I think the difference is only in the spark wire and spark plug connection. Is that correct?
Will both sizes go through the wire baffle seal cutout? https://www.aircraftspruce.com/catal...bafflem376.php
Are there implications I should know about choosing between the two sizes?
I think all the aircraft I have ever owned had the 3/4 inch nut. Is this the most common size?
Thanks.
Johan

[Caveman]

Originally Posted by Dorfie

Please help me understand the difference between the 5/8 and 3/4 inch wire to spark plug nuts.
Is the spark plug thread size into the cylinder head unaffected by the two different sizes?
I think the difference is only in the spark wire and spark plug connection. Is that correct?
Will both sizes go through the wire baffle seal cutout? https://www.aircraftspruce.com/catal...bafflem376.php
Are there implications I should know about choosing between the two sizes?
I think all the aircraft I have ever owned had the 3/4 inch nut. Is this the most common size?
Thanks.
Johan

This may help: http://www.aviationpros.com/article/...ion-spark-plug

Joe

[Dorfie]

Well, I found some more info in case it may be helpful to anyone. It is all contained in the spark plug number. The explanation (copied from ACS) is below. This link goes to ACS website's explanation. http://www.aircraftspruce.com/catalo...clickkey=59539

1. Resistor None--No Resistor R--Mil-Spec. Resistor-Erosion protection
2. Barrel Style None -- Unshielded E -- Shielded 5/8"-24 Thread
H -- Shielded 3/4"-20 Thread (All Weather Plug)
3. Mounting Thread -- Reach -- Hex Size B-18mm 13/16" / 2.06cm 7/8" / 2.22cm M--18mm 1/2"/1.27cm 7/8"/2.22cm
L-14mm 1/2"/1.27cm 13/16/2.06cm U*18mm 1-1/8"/2.85cm 13/16/2.06cm
J -- 14mm 3/8"/0.95cm 13/16/2.06cm
4. Heat Rating Position Low number--cold High number--hot
5. Electrode Design None-Conventional single E -- Two prong massive
N -- 4 prong massive
W -- Fine wire (Iridium) B --2 prong massive, Tangent to Center
P--Fine wire (Platinum)

I will be using REM40E spark plugs. It has 5/8 24 thread connector.

Johan

[Dorfie]

Originally Posted by Caveman

This may help: http://www.aviationpros.com/article/...ion-spark-plug

Joe

Thanks Joe,
Just what I was looking for. The description from the article copied below says it all;
"As a rule of thumb, the 5/8-24 connector is used on most normally aspirated engines that operate at less than 10,000 feet of altitude. The 3/4-20 harness, commonly referred to as a high altitude or all-weather harness due to its superior sealing characteristics, is used on virtually all turbocharged engines or normally aspirated engines that routinely operate at altitudes of 10,000 feet or higher. The 5/8-24 harness nut is installed using a 3/4-in. wrench, and the 3/4-20 harness nut is installed with a 7/8-in. wrench."

Thank you.
Johan