Spark Plug Socket Sizes: Which Size You Need
Spark plug socket sizes match the hex on the plug, and this guide shows the common sizes, how to read a listing, and which sets cover the sizes in your engine bay.
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A plug change stalls the moment the socket will not fit over the plug. The socket spins, the hex rounds, and the plug stays put while the rest of the job waits. Spark plug socket sizes are the match between the socket and the hex on the plug, and getting that match right is what turns a plug change into a short job. This guide shows the common sizes, how to read a listing, and which sets cover the sizes on the bench.
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Below: the sizes these sets cover, how to match a socket to a plug, and the sets themselves.
TecoTek 11-Piece Magnetic Spark Plug Socket Set
An 11-piece magnetic spark plug socket set with sockets in 5/8 in, 3/4 in, 13/16 in, 14 mm and 18 mm, a 3/8 in drive ratchet handle, a spark plug gapper, a universal joint and 3 in, 6 in and 10 in extension bars in a storage case.
Pros
- Sockets in 5/8 in, 3/4 in, 13/16 in, 14 mm and 18 mm
- Magnetic core holds the plug during install
- 3/8 in drive ratchet handle, gapper and universal joint included
- Heat treated chrome vanadium steel with mirror polish
Cons
- No torque wrench in the set
- Warranty term is 1 year
- No 9/16 in socket in the set
- No swivel socket stated in the listing
ELEAD 16-Piece Spark Plug Socket Set
A 16-piece spark plug socket set with 6 socket sizes, a 3/8 in drive torque wrench covering 5 to 45 lb-ft, Torx and E-Torx bit sockets, extensions and a universal joint.
Pros
- 6 socket sizes: 9/16 in, 5/8 in, 3/4 in, 13/16 in, 14 mm and 18 mm
- Torque wrench with 5 to 45 lb-ft range and click-stop feedback
- Spark plug gap tool covers 0.020 to 0.100 inch
- 12-point magnetic swivel sockets with 10 in extension bar
Cons
- Warranty term is 1 year
- No storage case stated in the listing
- No ratchet handle in the set
- No certification is stated
WORKPRO 3/8" Drive 6-Piece Magnetic Spark Plug
A 6-piece magnetic spark plug socket set with sizes 14 mm, 9/16 in, 5/8 in and 13/16 in, a full 360 swivel, a 1 mm thin wall and a 12-point design, with a lifetime warranty stated.
Pros
- Sizes 14 mm, 9/16 in, 5/8 in and 13/16 in
- Full 360 swivel for tight engine spaces
- 1 mm thin wall with 12-point grip
- Lifetime warranty stated
Cons
- No 3/4 in or 18 mm socket in the set
- No ratchet, gapper or torque wrench included
- No storage case stated in the listing
- Spec table lists NumberOfItems as 1 against a 6-piece title
LLNDEI 3/8-Inch Drive Magnetic Swivel Spark Plug
A 6-piece magnetic swivel spark plug socket set in 3/8 in drive, with sockets in 4 in, 6 in and 11 in lengths and a 2-year warranty term.
Pros
- 6 magnetic swivel sockets in 3/8 in drive
- Lengths of 4 in, 6 in and 11 in for varied access
- 2-year warranty term
- Weighs 2.75 lb per the spec table
Cons
- Title size list does not match the bullets size list
- No socket material stated
- No gapper, ratchet or extension bar in the set
- No certification is stated
Spark Plug Socket Sizes: The Common Sizes
The sets in this guide list sizes from 9/16 in to 18 mm, with metric sizes (14 mm, 18 mm) beside SAE sizes (9/16 in, 5/8 in, 3/4 in, 13/16 in).
| Size | Sets that list it |
|---|---|
| 9/16 in | ELEAD, LLNDEI, WORKPRO |
| 5/8 in | ELEAD, LLNDEI, TecoTek, WORKPRO |
| 3/4 in | ELEAD, TecoTek |
| 13/16 in | ELEAD, LLNDEI, TecoTek, WORKPRO |
| 14 mm | ELEAD, LLNDEI, TecoTek, WORKPRO |
| 18 mm | ELEAD, TecoTek |
Socket length matters where the plug sits deep in the head. The LLNDEI and WORKPRO sets list 4 in, 6 in and 11 in sockets, and the TecoTek set adds 3 in, 6 in and 10 in extension bars.
How to Match the Socket to the Plug
Start with the plug: the socket must match the hex on the plug, and the plug listing or the manual names the size. Then check the socket listing for the same size, the drive and the length. Each set in this guide uses a 3/8 in drive, so the drive matches a 3/8 in ratchet or torque wrench.
A magnetic core holds the plug in the socket while you lower it into the engine bay, so the plug does not drop on the way in. A swivel socket bends at the joint so the drive can sit at an angle to the plug, which helps where the plug sits behind other parts. Our comparison of magnetic vs rubber spark plug sockets covers how the plug is held, and the feeler gauge vs gap tool comparison covers gap checking.
A gap tool sets the plug gap before install: the ELEAD gapper covers 0.020 to 0.100 inch (0.6 to 2.4 mm). A torque wrench keeps the plug at the preset figure: the ELEAD wrench covers 5 to 45 lb-ft (6.8 to 61 N·m) with a click-stop that gives audible feedback at the preset torque. Check the manual for the gap and torque figures your plugs need.
Spark Plug Socket Sets for the Job
The sets below handle the sizing work: matching the socket to the plug hex, holding the plug on the way in, and setting the gap and the torque where the set includes the tools.
FAQ: garage tools
What size spark plug socket do I need?
The size that matches the hex on the plug. The sets in this guide cover 9/16 in, 5/8 in, 3/4 in, 13/16 in, 14 mm and 18 mm, so check the plug listing or the manual for the hex size, then pick a set that lists it. A socket that is too large slips and rounds the hex.
Do I need a magnetic spark plug socket?
A magnetic core holds the plug in the socket while you lower it into the engine bay, so the plug does not drop. The ELEAD, TecoTek, LLNDEI and WORKPRO sets in this guide all use a magnetic core, per their listings.
What does a swivel spark plug socket do?
A swivel socket bends at the joint so the drive can sit at an angle to the plug, which helps where the plug sits behind other parts. The ELEAD set lists 12-point magnetic swivel sockets, and the LLNDEI and WORKPRO sets list swivel sockets, with a full 360 swivel on the WORKPRO set. A universal joint gives a similar angle where the set includes one, as the ELEAD and TecoTek sets do.
How do I check the spark plug gap?
With a gap tool or a feeler gauge, before the plug goes in. The ELEAD set includes a spark plug gap tool that covers 0.020 to 0.100 inch (0.6 to 2.4 mm), and the TecoTek set includes a spark plug gapper. Check the plug maker’s gap figure in the manual, then set the gap to that figure.
How tight should a spark plug be?
Tight to the plug maker’s torque figure, not by feel alone. The ELEAD set’s torque wrench covers 5 to 45 lb-ft (6.8 to 61 N·m) with a click-stop that gives audible feedback at the preset torque. Check the manual for the figure your plugs need, then set the wrench to it.
Related: engine and shop equipment hub, our socket set types guide, the metric vs SAE socket set comparison and the best 3/8 in socket set. Also see the best 3/8 in torque wrench.
