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Description / Abstract:
FOREWORD
SECTIONAL COMMITTEE B18 on Dimensional Standardization of Bolts,
Nuts, Rivets, Screws, and Similar Fasteners was organized in March,
1922 under the procedure of the American Standards Association with
the Society of Automotive Engineers and The American Society of
Mechanical Engineers as joint sponsors.
Following the organization of the sectional committee,
subcommittees were appointed to facilitate development of standard
dimensions for the several types of bolts and nuts within the scope
of its activity. Subcommittee No. 2 after appraisal of the
requirements of industry, developed a proposed standard series of
bolt head and nut dimensions. This proposal was finally approved
and designated as an American Tentative Standard in February,
1927.
The June, 1930 meeting of Subcommittee No. 2 convinced the
majority of members that certain fundamental changes and additions
should be made to meet the requirements of industry. A
comprehensive study was made which resulted in the first revision
of the standard which was ultimately approved and designated as an
American Standard in March, 1933.
Further refinements were made in successive revised drafts of
the standard, dated November, 1937, May, 1938, March, 1939, and
March, 1940. A revision was approved and designated as an American
Standard in January, 1941.
Following reorganization of the sectional committee, February
20, 1947, Subcommittee No. 2 was asked to expand the standard on
head proportions into a complete product standard. Subgroups were
appointed to develop the product standards for bolts, nuts, cap
screws, and automotive hexagon head bolts. After numerous meetings
of the subgroups and Subcommittee No. 2 a proposed standard on
these products was prepared and submitted to the sectional
committee in April, 1950.
While this draft was under consideration, the Sectional
Committee received a proposal from the British Standards
Institution for unification of dimensions of products using the new
'unified' screw threads. The reactions of the Committee were not
favorable to the first proposals, but in its reply of December 22,
1949, .the Committee welcomed the opportunity of discussing the
proposals in order to explain and support its reactions. This
invitation was accepted and lead to a British-Canadian-American
Conference in New York, June 1-2, 1950.
It was agreed in the Conference that the essentials of
unification could be accomplished essentially by selection of
mutually satisfactory across-the-flats dimensions, since this would
permit the use of the same wrenches and since other features would
rarely affect interchangeability. The British delegation agreed on
the principle of selection of dimensions for unification on the
basis of existing American Standards. It was requested, however,
that consideration be given to suggestions for improvement of the
American Standards in certain instances. The British delegation,
therefore, was invited to select dimensions that they felt would be
needed in British standards and in standardization of defense
products, with the understanding that the Canadian and American
delegations would raise questions where they were not in agreement.
After due consideration, across-the-flats dimensions were selected
for hexagon products.
It then became the responsibility of the respective
standardizing bodies to implement the Conference recommendations.
In its meeting of October 13, 1950, the Subcommittee agreed to
incorporate in American Standards the conference recommendations on
1/4 inch hexagon bolts,
5/8 inch cap screws and automotive bolts,
5/16 and 3/8 inch regular hexagon and square
nuts, and 7/16 inch light and regular hexagon
and square nuts. At a subsequent meeting of Subcommittee 2 on
February 2, 1951. further changes were made in order to combine the
light and regular series of nuts and to combine the automotive
hexagon head bolt, hexagon head cap screw, and regular close
tolerances- bait.. The dimensions of these combined series were
submitted to industry for comment in a draft dated March, 1951. In
the meantime, British drafts based upon Institution proposed a
London Conference to conclude the activity by making certain
hexagon bolts and nuts completely interchangeable. These meetings
were held April 26-27, 1951, The British, Chadian, and American
delegations unanimously agreed to recommend to their respective
standards bodies that dimensions of hexagon products that are shown
in bold face in this standard be designated as 'unified,' although
it was agreed that individual countries might establish smaller
tolerances within those limits to govern local production of the
products, providing the acceptance limits established for the
unified products are not reduced. Other items in the same tables
are based upon formulas that have been accepted and published by
the British for sizes outside of the range listed in their
standard.
In its meeting of June 8, 1951, Subcommittee No. 2 reaffirmed
its acceptance of the unified dimensions since they corresponded
with those in the March, 1951 draft. However, the Subcommittee
reversed previous action on square bolts and nuts which were not
involved in unification and they attempted to select better
nomenclature for the unified products. A revised draft
incorporating these changes was submitted to the Subcommittee in
July, 1951, and a further revision was made in a meeting of August
10, 1951 because of continued dissatisfaction with the nomenclature
that was previously selected. A final draft using the nomenclature
"Finished Hexagon Bolts and Nuts" and containing numerous editorial
changes was submitted for letter ballot in September, 1951.
Following approval by the sectional committee. and the sponsors
the proposal was presented to the American Standards Association
for approval and designation as an American Standard. This was
granted on March 24, 1952. In taking this action, the sectional
committee recognized there was need for additional refinements, but
it felt that they should be included in a subsequent revision
because of the urgency for mutual defense purposes of a standard
embodying the ABC agreements. Upon issue of the 1952 revision,
therefore, work was started immediately to make these minor
improvements. Inconsistencies were removed in respect to fillets,
improvements were made in the Length tolerances of heavy bolts, and
other corrections and clarifications of an editorial nature were
incorporated. The most noteworthy editorial change was a decision
to combine the B18.2 standards on Hexagon Cap Screws and Square
Head Set Screws with the B18.6 standards on Slotted Head Cap Screws
for publication in a separate standard. Since the unified "Hexagon
Head Cap Screws", and "Finished Hexagon Bolts" have identical
requirements in the size range in which they overlap, the
information will now be available in two publications to replace
the separate tables previously included in the B18.2 standard.
Following necessary approvals, the revision was submitted to the
American Standards Association. It was approved and designated as
an American Standard February 2, 1955.
The proposed revision of B18.2 dated May 20, 1959 was approved
by the Committee, the sponsors and the American Standards
Association, and it was designated as an American Standard on April
18, 1960.