Hex key (English Wikipedia)

Rybczynski 2000, pp. 79–81. Rybczynski, Witold (2000), One Good Turn: A Natural History of the Screwdriver and the Screw, Scribner, ISBN 978-0-684-86729-8, LCCN 00036988, OCLC 462234518. Various republications (paperback, e-book, braille, etc).
Hallowell 1951, pp. 51–52. Hallowell, Howard Thomas Sr (1951), How a Farm Boy Built a Successful Corporation: An Autobiography, Jenkintown, Pennsylvania, USA: Standard Pressed Steel Company, LCCN 52001275, OCLC 521866.
Hallowell 1951, p. 51. Hallowell, Howard Thomas Sr (1951), How a Farm Boy Built a Successful Corporation: An Autobiography, Jenkintown, Pennsylvania, USA: Standard Pressed Steel Company, LCCN 52001275, OCLC 521866.
Hallowell 1951, p. 52. Hallowell, Howard Thomas Sr (1951), How a Farm Boy Built a Successful Corporation: An Autobiography, Jenkintown, Pennsylvania, USA: Standard Pressed Steel Company, LCCN 52001275, OCLC 521866.
Hallowell 1951, pp. 54, 57–59. Hallowell, Howard Thomas Sr (1951), How a Farm Boy Built a Successful Corporation: An Autobiography, Jenkintown, Pennsylvania, USA: Standard Pressed Steel Company, LCCN 52001275, OCLC 521866.
Hallowell 1951, p. 54. Hallowell, Howard Thomas Sr (1951), How a Farm Boy Built a Successful Corporation: An Autobiography, Jenkintown, Pennsylvania, USA: Standard Pressed Steel Company, LCCN 52001275, OCLC 521866.

mdmetric.com

"MARYLAND METRICS - TECHNICAL INFORMATION and DATA - Hexagon sockets (DIN 912, ISO 4762, DIN 6912, DIN 7984, DIN 7991, DIN 913, 914/5/6, ISO 4026, 4027/8/9, ISO 7379, ISO 7380, K 323)" (PDF). Archived from the original (PDF) on 21 August 2018. Retrieved 25 April 2020.

ratgeberrecht.eu

solidinfo.se

unbrako.com; Varumärke - UNBRAKO (solidinfo.se)

tme.eu

"Bossard Hex socket keys" (PDF). Retrieved 24 September 2023.

unbrako.com

unbrako.com; Varumärke - UNBRAKO (solidinfo.se)

web.archive.org

Alloy Artifacts, Various Tool Makers (section on Allen Manufacturing Company), archived from the original on 30 December 2011, retrieved 25 January 2012.
"MARYLAND METRICS - TECHNICAL INFORMATION and DATA - Hexagon sockets (DIN 912, ISO 4762, DIN 6912, DIN 7984, DIN 7991, DIN 913, 914/5/6, ISO 4026, 4027/8/9, ISO 7379, ISO 7380, K 323)" (PDF). Archived from the original (PDF) on 21 August 2018. Retrieved 25 April 2020.
Premiere ball end tools, Bondhus Corporation, archived from the original on 19 March 2006

worldcat.org

Pilloton, Emily (2020). Girls garage: how to use any tool, tackle any project, and build the world you want to see. Kate Bingaman-Burt. San Francisco, California. p. 110. ISBN 978-1-4521-6637-7. OCLC 1155316269.{{cite book}}: CS1 maint: location missing publisher (link)
Rybczynski 2000, pp. 79–81. Rybczynski, Witold (2000), One Good Turn: A Natural History of the Screwdriver and the Screw, Scribner, ISBN 978-0-684-86729-8, LCCN 00036988, OCLC 462234518. Various republications (paperback, e-book, braille, etc).
Hallowell 1951, pp. 51–52. Hallowell, Howard Thomas Sr (1951), How a Farm Boy Built a Successful Corporation: An Autobiography, Jenkintown, Pennsylvania, USA: Standard Pressed Steel Company, LCCN 52001275, OCLC 521866.
Hallowell 1951, p. 51. Hallowell, Howard Thomas Sr (1951), How a Farm Boy Built a Successful Corporation: An Autobiography, Jenkintown, Pennsylvania, USA: Standard Pressed Steel Company, LCCN 52001275, OCLC 521866.
Hallowell 1951, p. 52. Hallowell, Howard Thomas Sr (1951), How a Farm Boy Built a Successful Corporation: An Autobiography, Jenkintown, Pennsylvania, USA: Standard Pressed Steel Company, LCCN 52001275, OCLC 521866.
Hallowell 1951, pp. 54, 57–59. Hallowell, Howard Thomas Sr (1951), How a Farm Boy Built a Successful Corporation: An Autobiography, Jenkintown, Pennsylvania, USA: Standard Pressed Steel Company, LCCN 52001275, OCLC 521866.
Hallowell 1951, p. 54. Hallowell, Howard Thomas Sr (1951), How a Farm Boy Built a Successful Corporation: An Autobiography, Jenkintown, Pennsylvania, USA: Standard Pressed Steel Company, LCCN 52001275, OCLC 521866.
Brewer, Dennis C. (2012). Build your own free-to-air (FTA) satellite TV system. New York: McGraw-Hill. p. 13. ISBN 978-0-07-177516-8. OCLC 778421711.