MLA style:

"T20". FullForms. FullForms.com, 2019. Web. 20 Feb. 2019
<https://fullforms.com/T20/Torx-screw-head-size-(0.151-inch-or-3.86-millimeter)/13773>.

Chicago Style:

FullForms.com, FullForms, 2019. "T20" Accessed February 20, 2019.
https://fullforms.com/T20/Torx-screw-head-size-(0.151-inch-or-3.86-millimeter)/13773

APA style:

T20. (n.d.). In FullForms. Retrieved from https://fullforms.com/T20/Torx-screw-head-size-(0.151-inch-or-3.86-millimeter)/13773

Harvard style:

T20. 2019. FullForms. Retrieved 20 February, 2019, from https://fullforms.com/T20/Torx-screw-head-size-(0.151-inch-or-3.86-millimeter)/13773

Please refer to the appropriate style manual if you have any questions.