Bsi bs au 025 1964 (2000)

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BRITISH STANDARD AUTOMOBILE SERIES

BS AU 25:1964
Sup ers edes S. M. M. T.
Standard No .

Specification for

Towing hook for use
between trailers
of 5–14 tons gross
weight and towing
vehicle

UD C 62 9 . 1 1 . 0 1 3 . 5 : 62 9 . 1 1 . 0 1 3 . 81

51


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BS AU 25:1964

This Britis h S tandard, having
b een ap p roved b y the
Automob ile I ndus try
S tandards C ommittee and
endors ed b y the C hairman
of the E ngineering D ivis ional

C ouncil, was p ub lis hed under
the authority of the General

Amendments issued since publication

C ouncil of the I ns titution on
1 5 June 1 9 64

© BS I 0 2 - 2 0 0 0

The following BS I reference
relates to the work on this
s tandard:
C om mittee reference AUE /-

ISBN 0 580 34548 3

Amd. No.

D ate

C omments


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BS AU 25:1964

Contents
Page

Foreword

© BS I 0 2 - 2 00 0

ii

1

S cop e

1

2

Materials

1

3

D imens ions

1

4

D es ign

1

5

Mounting

1

6

Marking

1

Figure 1 — Towing hook, indicating s afety catch

2

Figure 2 — Towing hook

3

i


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BS AU 2 5 : 1 964

Fore word

This British Standard, which is published under the authority of the

Automobile Industry Standards Committee of the BSI, is based upon
data- sheet SMMT 51 : 1 957 of the Society of Motor Manufacturers and
Traders Ltd. The requirements of this standard, which relate only to vehicles
used on the public highways, are intended to ensure the maximum degree of
interchangeability between commercial and Government department and
Services standards.
The material specifications are for the minimum qualities acceptable, and do not
exclude the use of other materials provided that these are at least equal in quality
so that road safety is not impaired.
This standard should be used in conj unction with BS AU 29

1)

. The hook has been

designed to accommodate a drawbar eye of 2 in internal diameter and 1 ; in stock,
or 3 in internal diameter and 1 C in stock.
The standard applies to connections to trailers of 5 – 1 4 tons gross weight.
The specification for a towing hook for connections to trailers of 5 – 35 tons gross
weight is given in BS AU 27
BS AU 24
NOTE

3)

2)

, and for trailers of 2 – 5 tons gross weight in

.

If it is required to convert the figures in this standard from British units into metric units it

Conversion factors and
tables, be used. Attention is drawn to BS 2856, Precise conversion of inch and metric sizes on
engineering drawings
is recommended that the conversion factors and tables contained in BS 350,

A British Standard does not purport to include all the necessary provisions of a
contract. Users of British Standards are responsible for their correct application.
C omp liance with a British S tand ard d oe s no t of itse lf confe r immunity
from le gal ob ligatio ns.

S ummary of p age s

This document comprises a front cover, an inside front cover, pages i and ii,
pages 1 to 3 and a back cover.
This standard has been updated (see copyright date) and may have had
amendments incorporated. This will be indicated in the amendment table on the
inside front cover.

BS AU 29, “Drawbar eyes and forecarriage pins for connection between trailers of 5 – 35 tons
gross weight and towing vehicle”.
2)
BS AU 27, “ Towing hook for use between trailers of 5 – 35 tons gross weight and towing vehicle ”.
3)
BS AU 24, “Towing connections for trailers of 2 – 5 tons gross weight ”.

1)

ii

© BSI 02- 2000


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BS AU 25:1964

1 Scope

5 Mounting

This British Standard specifies the basic

The hook shall be mounted with four bolts, C in

dimensions and quality of materials for a towing

diameter, at 4 in

hook and its mounting, for use in connections

interchangeable in mounting with certain

×

4 in centres. This renders it

between a towing vehicle and a trailer of 5 – 1 4 tons

Government department and Services standard

gross weight.

hooks.

The gross weights refer to gross laden train weights

Bolts and nuts shall comply with:

where more than one trailer is drawn.

i) BS 1 083,

2 Materials

ii) BS 1 768,

The hook shall be made from a material of quality
not less than BS 970. En 5(N)

or

4)

threaded UNF, code symbol R5) .

The nuts shall be secured either by peening the end
of the bolt or by fitting a positive locking device such

as a safe locking nut or a slotted nut and split pin.

3 Dimensions

6 Marking

Dimensions shall be as shown in Figure 1 and
Figure 2.
NOTE

threaded BSF, code symbol R,

The following wording, in clear lettering B in high,
raised or impressed, shall be marked on each towing

The dimensions specified are based upon a forged hook,

and have been calculated on the basis of the total yield strength

hook:

being equal to two thirds of the gross weight being towed. It is

“TO TOW 1 4 TONS GROSS” on one side, and on

necessary that any other parts not covered by this standard,

the other side “BS AU 25”.

connecting the coupling to, the towing vehicle shall have a

similar strength.

4 Design
An efficient safety catch, preferably of the automatic
or semi- automatic type, shall be provided as
indicated in Figure 1 to prevent accidental
detachment of the drawbar from the hook.
The hook shall be so designed that a bar 1

23
32

in

diameter, when held vertically, may be passed
freely between the inside faces of the hook with the
catch held back to clear (see Figure 1 ) .

4)
5)

BS 1 083, “Precision

BS 1 768, “Unified

© BSI 02- 2000

hexagon bolts, screws and nuts”.
precision hexagon bolts, screws and nuts (UNC and UNF thread-normal series)”.

1


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All dimensions are in inches

BS AU 2 5 :1 964

2
Figure 1 — Towing hook, indicating safe ty catch

© BSI 02 - 2 000


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All dimensions are in inches

© BSI 02 - 2 000

Figure 2 — Towing hook

BS AU 25:1964

3


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BS AU 25:1964

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