Cycling Equipment · Public discussion

tapered square standards

Martin Trautman · 2003-02-11T14:00:19+00:00

Hi all, do you know any overview of tapered squares of bottom brackets and cranks? I got one here that is e.g. +---------- +/////////| | ) +====\ ) ^ | || ) M | || ) v +====/ ) | ) +\\\\\\\\\| +---------- ^W_o ^W_i huh, this asci art is pretty ugly. Sorry, this is NOT a thread on the spindle, but shall be read as a slightly tapered square (/// \\\). Check e.g. http://www.sheldonbrown.com/harris/images/ta-bb-axles.gif for a better drawing - the picture above shows the crank screw thread as well. An old bottom bracket here has e.g. an outer size W_o = 13.0 mm, inner size W_i = 14.0 mm, and a square length L = 15.0 mm This square length L is measured from W_o to W_i, which is slightly biased. The angle of the square is alpha = arc sin ((W_o - W_i) / L), alpha = 3.8 deg The horizontal length of L thus is L' = L * cos alpha = 14.97 mm For those small angles L and L' can be assumed to be identical. The thread for the crank screw here is M12x1 - thus you might name this square as 12/13/14/15 :-) Other spindles are not drilled and threaded for screws, but have a thread for nuts - yet another standard. What are the typical sizes of e.g. current Shimano (not splined), Campa etc. cranks or bottom brackets, JIS or ISO square? AFAIK both JIS (e.g. Shimano) and ISO (e.g. Campa) share an angle of 2 deg; JIS is 12.65 mm somewhere, Campa is smaller somehow. I've found Sheldon's different dust cap sizes of Campa 22 x 1 mm (and others) e.h. 22.8 x 1 mm Stronglight 23 x 1 mm Lampert 7/8" x 24 tpi ( = 22.22 x 1.05 mm) ... but nothing on square 'standards' and different variations. Which dimensions are there around? Best regards Martin

Started by Martin Trautman · 11 February 2003 · Last activity 12 February 2003 · 8 posts · 1,364 views

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Original section: Cycling Equipment
Published: 11 February 2003
Last activity: 12 February 2003
Original author: Martin Trautman
Posts: 8
Discussion status: Public discussion
Total views: 1,364
Views / 30 days: 0
Topics: Bottom brackets Taper and peaking Cranksets

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Original post
Martin Trautman
Archived post

11 February 2003, 14:00 UTC #1

Hi all,
do you know any overview of tapered squares of bottom brackets and cranks?
I got one here that is e.g.
+---------- +/////////|
| )
+====\ ) ^ | || ) M | || ) v +====/ )
| )
+\\\\\\\\\| +----------
^W_o ^W_i
<--- L --->
huh, this asci art is pretty ugly. Sorry, this is NOT a thread on the spindle, but shall be read as
a slightly tapered square (/// \\\). Check
e.g. sheldonbrown.comta bb axles.gif for a better drawing - the picture
above shows the crank screw thread as well.
An old bottom bracket here has e.g. an outer size W_o = 13.0 mm, inner size W_i = 14.0 mm, and a
square length L = 15.0 mm
This square length L is measured from W_o to W_i, which is slightly biased. The angle of the square
is alpha = arc sin ((W_o - W_i) / L), alpha = 3.8 deg
The horizontal length of L thus is L' = L * cos alpha = 14.97 mm For those small angles L and L' can
be assumed to be identical.
The thread for the crank screw here is M12x1 - thus you might name this square as 12/13/14/15 :-)
Other spindles are not drilled and threaded for screws, but have a thread for nuts - yet
another standard.
What are the typical sizes of e.g. current Shimano (not splined), Campa etc. cranks or bottom
brackets, JIS or ISO square?
AFAIK both JIS (e.g. Shimano) and ISO (e.g. Campa) share an angle of 2 deg; JIS is 12.65 mm
somewhere, Campa is smaller somehow.
I've found Sheldon's different dust cap sizes of Campa 22 x 1 mm (and others)
e.h. 22.8 x 1 mm Stronglight 23 x 1 mm Lampert 7/8" x 24 tpi ( = 22.22 x 1.05 mm)
... but nothing on square 'standards' and different variations. Which dimensions are there around?
Best regards Martin

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Martin Trautman
Archived post

11 February 2003, 14:00 UTC #2

Martin Trautmann said:
This square length L is measured from W_o to W_i, which is slightly biased. The angle of the
square is alpha = arc sin ((W_o - W_i) / L), alpha = 3.8 deg
oops - I feel that in general the angel is not given in total, put per side. Thus the angle will be
arc sin ((W_o - W_i) / 2 L) = 2 deg
Quoted message said:
AFAIK both JIS (e.g. Shimano) and ISO (e.g. Campa) share an angle of 2 deg; JIS is 12.65 mm
somewhere, Campa is smaller somehow.
from news:<[email hidden]> I found:
ISO: L_right = 18 +0.5/-0 mm L_left = 16 +0.5/-0 mm
Dimension across flat 1.5mm from end: 12.6mm +0.02-0.05 Spindle end to bolt seat: Loose: 3mm
Tightened: 1.5mm min. Crank fixing threads: Bolt-type M8x1 Nut-type M10x1.25 Crank bolt or nut
size 14mm Dustcap threads M22x1
what/where are crank fixing threads?
Best regards Martin

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Paul Southworth
Archived post

11 February 2003, 15:30 UTC #3

In article said:

from news:<[email hidden]> I found:
ISO: L_right = 18 +0.5/-0 mm L_left = 16 +0.5/-0 mm
Dimension across flat 1.5mm from end: 12.6mm +0.02-0.05 Spindle end to bolt seat: Loose: 3mm
Tightened: 1.5mm min. Crank fixing threads: Bolt-type M8x1 Nut-type M10x1.25 Crank bolt or nut
size 14mm Dustcap threads M22x1
what/where are crank fixing threads?
It's the bolt or nut that holds the crank arm on. Most are bolt-style today. M8x1 is the size used
on square-taper spindles.
--Paul

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Martin Trautman
Archived post

11 February 2003, 16:00 UTC #4

Paul Southworth said:
In article said:

from news:<[email hidden]> I found:
ISO: L_right = 18 +0.5/-0 mm L_left = 16 +0.5/-0 mm
Dimension across flat 1.5mm from end: 12.6mm +0.02-0.05 Spindle end to bolt seat: Loose: 3mm
Tightened: 1.5mm min. Crank fixing threads: Bolt-type M8x1 Nut-type M10x1.25 Crank bolt or
nut size 14mm Dustcap threads M22x1
what/where are crank fixing threads?
It's the bolt or nut that holds the crank arm on. Most are bolt-style today. M8x1 is the size
used on square-taper spindles.
Thanks - so the 14 mm is the outer width (the literal German translation would be key width) of the
nut or six edge bolt.
I was confused by standard non-bicycle versions, with 13 mm for M8 six edge bolts and 6 mm for M8
Inbus / ISO 4762 or 17 mm for M10 nuts.
Best regards Martin

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Paul Southworth
Archived post

11 February 2003, 16:33 UTC #5

In article said:
Paul Southworth said:
In article said:

from news:<[email hidden]> I found:
ISO: L_right = 18 +0.5/-0 mm L_left = 16 +0.5/-0 mm
Dimension across flat 1.5mm from end: 12.6mm +0.02-0.05 Spindle end to bolt seat: Loose: 3mm
Tightened: 1.5mm min. Crank fixing threads: Bolt-type M8x1 Nut-type M10x1.25 Crank bolt or
nut size 14mm Dustcap threads M22x1
what/where are crank fixing threads?
It's the bolt or nut that holds the crank arm on. Most are bolt-style today. M8x1 is the size
used on square-taper spindles.
Thanks - so the 14 mm is the outer width (the literal German translation would be key width) of the
nut or six edge bolt.
14mm is the size of the socket you use to tighten the bolt.
15mm also exists but not as common.
--Paul

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A Muzi
Archived post

12 February 2003, 05:00 UTC #6

"Martin Trautmann" <[email hidden]> wrote in message
"]news:[email hidden]...
Quoted message said:

Hi all,
do you know any overview of tapered squares of bottom brackets and cranks?
I got one here that is e.g.
+---------- +/////////|
| )
+====\ ) ^ | || ) M | || ) v +====/ )
| )
+\\\\\\\\\| +----------
^W_o ^W_i
<--- L --->
huh, this asci art is pretty ugly. Sorry, this is NOT a thread on the spindle, but shall be read
as a slightly tapered square (/// \\\). Check
e.g. sheldonbrown.comta bb axles.gif for a better drawing - the picture
above shows the crank screw thread as well.
An old bottom bracket here has e.g. an outer size W_o = 13.0 mm, inner size W_i = 14.0 mm, and a
square length L = 15.0 mm
This square length L is measured from W_o to W_i, which is slightly biased. The angle of the
square is alpha = arc sin ((W_o - W_i) / L), alpha = 3.8 deg
The horizontal length of L thus is L' = L * cos alpha = 14.97 mm For those small angles L and L'
can be assumed to be identical.
The thread for the crank screw here is M12x1 - thus you might name this square as 12/13/14/15 :-)
Other spindles are not drilled and threaded for screws, but have a thread for nuts - yet another
standard.
What are the typical sizes of e.g. current Shimano (not splined), Campa etc. cranks or bottom
brackets, JIS or ISO square?
AFAIK both JIS (e.g. Shimano) and ISO (e.g. Campa) share an angle of 2 deg; JIS is 12.65 mm
somewhere, Campa is smaller somehow.
I've found Sheldon's different dust cap sizes of Campa 22 x 1 mm (and others)
Quoted message said:
T.A. 22.8 x 1 mm Stronglight 23 x 1 mm Lampert 7/8" x 24 tpi ( = 22.22 x 1.05 mm)
... but nothing on square 'standards' and different variations. Which dimensions are there around?
Best regards Martin
That is an early variant of inexpensive square-taper crank, made when melt-forged aluminum cranks
were new and the alloys weren't as developed as now. Those were made by Takagi and SR-Sakae. Some
but not all sizes are still available as spares.
It should have a marking for size, like possibly 3H, which would be a big help if you are looking
for a new one.
I can't do ascii art either, but I have a camera:
yellowjersey.org3SPINDLE.JPG Is it the one on the left?
--
Andrew Muzi yellowjersey.orgyellowjersey.org Open every day since 1 April 1971

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Martin Trautman
Archived post

12 February 2003, 09:30 UTC #7

A Muzi said:
That is an early variant of inexpensive square-taper crank, made when melt-forged aluminum cranks
were new and the alloys weren't as developed as now. Those were made by Takagi and SR-Sakae. Some
but not all sizes are still available as spares.
It should have a marking for size, like possibly 3H, which would be a big help if you are looking
for a new one.
I can't do ascii art either, but I have a camera:
yellowjersey.org3SPINDLE.JPG Is it the one on the left?
Yeah, I'd say so. How about the measured sizes of those models?
Kind regards Martin

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Martin Trautman
Archived post

12 February 2003, 13:00 UTC #8

Martin Trautmann said:
Quoted message said:
AFAIK both JIS (e.g. Shimano) and ISO (e.g. Campa) share an angle of 2 deg; JIS is 12.65 mm
somewhere, Campa is smaller somehow.
ISO: L_right = 18 +0.5/-0 mm L_left = 16 +0.5/-0 mm
Dimension across flat 1.5mm from end: 12.6mm +0.02-0.05 Spindle end to bolt seat: Loose: 3mm
Tightened: 1.5mm min.
Yet another source claimed that the squares of Campa, Mavic and Stronglight (ISO) are smaller than
Shimano and Suntour (JIS) with the result that JIS cranks will move about 4.5 mm further in.
This may conflict with the end of the square and result in a loose fit or braking stress. for ISO
cranks on JIS squares there's less contact area between crank and spindle, since the crank does not
slip perfectly on the spindle. The result again is a higher risk of braking the crank.
But assuming those 4.5 mm and 2 deg, ISO is about 0.3 mm smaller than JIS (2 * sin 2 * 4.5 = 0.3)?
Kind regards Martin

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