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thread diameter, a thread pitch of
1.5mm and a thread length of
45mm.

A common mistake some folks

make is to incorrectly identify nut
or bolt sizes, confusing hex head
size with thread size. The size of the
fastener (thread area diameter)
refers to the diameter of the thread-
ed area (threaded hole in a nut or
threaded shank on a stud or bolt).
The wrench size required to service
the fastener does not indicate fas-
tener size. The width of the hex
head (let’s say a nut requires a 3/4-
inch or 19mm socket) has no bear-
ing whatsoever on fastener size. For
example, if the threaded area is

12mm in diameter, the nut or stud
is a 12mm size, not a 19mm (refer-
ring to the size of socket required).
When sizing any fastener, ignore the
service end (hex head). It’s only the
diameter of the thread area that
indicates the fastener’s size.

THREAD PITCH

All Toyota vehicles feature metric

wheel fasteners. However, simply to
provide a better understanding of
threaded fasteners, we’ll offer an
overview of both “inch” and metric
formats.

When using inch format, the

thread pitch number indicates the
number of threads along a one-inch

length of the shank. For example, a
1/2-inch x 20 wheel stud is 1/2-inch
in diameter, and has a thread count
of 20 threads per inch of shank
length.

When using a metric format, the

first number indicates the thread
shank diameter in millimeters
(12mm, 14mm, etc.). However, met-
ric thread pitch numbers indicate
the distance between threads. For
example, a thread pitch of 1.25 indi-
cates that the distance between two
adjacent threads is 1.25mm. If the
thread pitch is 1.50, the distance
between threads is 1.5mm. The last
number of a stud or bolt size indi-
cates length. A size of 14mm x 1.5 x
35, for example, indicates a stud or
bolt that is 14mm in diameter, a
thread pitch of 1.5mm and a shank
length of 35mm.

In inch format, the higher the

pitch number, the “finer” the
threads (more threads per inch of
shank length). Using a 1/2-inch
diameter fastener as an example, a
thread pitch of 13 is “coarse,” while
a thread pitch of 20 is considered
“fine.” Using a 1/4-inch diameter
fastener as an example, a thread
pitch of 20 is considered coarse,
while a 28 pitch is considered fine.
Basically, in inch format, each fas-
tener thread diameter size offers
two choices — coarse or fine. With
regard to wheel fasteners, the
threads are always “fine.”As com-
pared to coarse threads, this pro-
vides increased bolt strength and
potential clamping load. If a wheel
fastener is 7/16-inch diameter, the
thread pitch will be 20. If 1/2-inch
diameter, thread pitch will be 20. If
9/16-inch diameter, thread pitch
will be 18. In metric format, the

INSTALLING ALLOY WHEELS

Thread pitch gauges (available in both inch and metric formats) pro-

vide an easy and accurate method of determining the wheel stud

thread pitch, eliminating any guesswork.

higher the number, the more
“coarse” the thread pitch. For exam-
ple, a 1.0 pitch is “very fine,” a 1.25
pitch is “medium fine,” a 1.5 pitch is
“medium” and a 1.75 pitch is
“coarse.” Metric wheel fasteners will
commonly either feature a 1.25 or
1.5 thread pitch, regardless of
thread diameter.

LENGTH

The amount of thread engagement

between the stud and nut (or wheel
bolt to hub) is critical. At the mini-
mum, thread engagement length
must be equal to or greater than the
diameter of the fastener. In other
words, if the stud is 12mm in diam-
eter, the nut must engage onto the
stud by at least 12mm. If not, either
a longer stud or longer nut must be
used (if a longer nut is needed, the
nut must protrude further through
the wheel hole to meet the stud).
Use of longer nuts is possible when
the nut features an extended shank
that offers greater thread length.
This will vary depending on nut
style. If this isn’t feasible, a longer
stud must be used.

When using wheel bolts or capped

(enclosed) nuts, care must be taken
to avoid bottoming the bolt or nut.
For example, if the stud offers one
inch of exposed length for nut
engagement, but the threaded hole
in the nut is only 3/4-inch deep, the
nut will bottom-out on the stud and
will not clamp the wheel against the
hub.

In order to accurately identify the

thread diameter, pitch and length of
any wheel fastener, you can handle
this by obtaining a total of three
readily available tools: a combina-
tion bolt/nut sizing card (these are

hard plastic and are available to
cover both inch and metric sizes)
and two thread pitch gauges (one
inch and one metric). That’s all you
need to quickly and accurately read
any wheel bolt or nut without any
guesswork.

BOLT CIRCLE

The term “bolt circle” or “bolt pat-

tern” refers to the diameter of the
circle formed by the wheel or hub
fastener mounting locations. Toyota
models use bolt circles of 100mm
(3.93 inches), 114.3mm (4.5 inches)
and 139.7mm (5.5 inches). A desig-
nation of 4x100 indicates a wheel
with four bolt holes, with the holes
positioned to create a 100mm circle
(when measured through the cen-
terline of all holes). A wheel desig-
nation of 5x114.3 indicates a five-

bolt wheel that provides a bolt circle
of 114.3mm (4.5 inches).

If you want to manually measure a

bolt circle,here are some easy methods:

1. With a four-bolt or six-bolt pat-

tern, measure from the center of
one stud (at the hub) or wheel hole,
to the center of an opposing stud or
wheel hole.

2. With a five-bolt pattern, orient

the hub or wheel to place one fas-
tener location at 12-o’clock.
Measure from the center of the 12-
o’clock location to a horizontal line
drawn across the bottom of the two
bottom studs or wheel holes.

Bolt circle information is usually

provided on the wheel (look at the
rear of the wheel, the information
should be stamped or cast on the

O Y O TA’ S

U P P O R T

U T O M O T I V E

E PA I R

INSTALLING ALLOY WHEELS

A plastic sizing disc provides multiple holes, each labeled for bolt cir-

cle reference. Simply align the disc onto the wheel (or onto the hub

studs) until all of the hub or wheel holes align on the disc, and read the

numbers on the disc to identify the bolt circle. For illustrative purpos-

es, we’ve marked the holes that align to the wheel shown here. Note