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Is a 5/8 and 16mm ALWAYS the same thing?

expatriated

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Mar 22, 2009
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Both my bike and my Toyota manuals say use a 16mm sparkplug socket. I have a cheaper one (marked 16mm) but when I go to look for an upgrade from SO and others, I see nothing but 5/8. Before I shell out the cash, these pricey 5/8's will work exactly like the 16mm? Or am I missing something on SO's website?

Also, anyone prefer the magnetic sparkplug sockets over the rubber insert ones? I'm thinking of going for the magnetic one--any thoughts?

Thanks.
 
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pmohr

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Jul 3, 2009
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Maryville, TN
5/8" is slightly under 16mm (15.8 according to google), but I've personally never seen a plug that a 5/8", 13/16", or 14mm didn't fit. FWIW the Nissan FSMs say a 16mm magnetic plug socket, which is interesting, though the plugs have a 5/8" hex:
FSM-plug-socket.PNG




I would imagine the magnetic ones would be nice because you don't have to worry about the rubber insert staying stuck on the plug, but I've never actually used one.
 

ImportTuner

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I've been working on cars since the 60's .. first time I've heard of 16mm; now 5/8, yes :)
Guess I haven't been reading the manual ..
 

Monte

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16mm spark plug sockets are often marked 5/8" too , also 13/16" spark plug sockets say 20,8 mm sometimes 21mm too.
 

Tlag

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Jan 17, 2009
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151
Speaking of almost the same...

5/16 is .313", 8mm is .315"
7/16 is .438", 11mm is .433"
3/4 is .750, 19mm is .748"
 

APEowner

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Oct 2, 2009
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Sunny, New Mexico
The spark plug manufacturer I have as a client makes it's plugs conform to the ISO standard which specifies a 16mm hex. They also make a spark plug socket designed to the applicable ISO standard for 16mm hex head fasteners but, it's marked 5/8. I suspect it's like the small headphone jacks that everyone calls 1/8" but are really 3.5mm.
 
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NAYLOR

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Jan 5, 2008
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Both my bike and my Toyota manuals say use a 16mm sparkplug socket. I have a cheaper one (marked 16mm) but when I go to look for an upgrade from SO and others, I see nothing but 5/8. Before I shell out the cash, these pricey 5/8's will work exactly like the 16mm? Or am I missing something on SO's website?

Also, anyone prefer the magnetic sparkplug sockets over the rubber insert ones? I'm thinking of going for the magnetic one--any thoughts?

Thanks.

I use a 5/8 with rubber on my Tacoma. Never had any problems.
 

vc-onthepc

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Sep 12, 2008
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maryland
Not excatly part of this topic but id like to add that the rubber insert style spark plug sockets actually can cause a misfire by depositing crud on the insulator portion of the plug . This is evidenced by removing the plug and youll see grey light brown streaks on the insulator .

I only learned this by my experiance with CNG fueled transit buses . They have very tempermental ignition systems.

When using Snap-On magnectic spark plug sockets be very careful ...when you are installing the plug ,If you catch it on something the plug will fall out .If it does dont forget to recheck the gap !!!

Also when installing coated plugs with platnuim or unobtainium or whatever there made out of make sure that it its flaking off in the ground strap be sure file it down or you will have a misfire .

Dont forget to make sure the platnuim tips are centered on the ground strap
off center chance for miss ...If its not attached fully throw plug away and get another
 

Here2Learn

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Oct 27, 2009
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Alabama
In some various Kawasaki manuals, it shows a 21mm spark plug tool to use on the 13/16" NGK spark plugs. Well, they are listed as 13/16" on the USA NGK site. :)
 

UK Steve

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Mar 13, 2009
Messages
171
Japanese M/cycles use 13mm, 14mm, 16mm, 18mm & 20.8mm, some BMW M series engines use the 18mm plug (very tight to get into most sockets need grinding (but not all).
As for the magnetic plug socket keep well away from ECU's they just don't get on very well.........
 
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