The buttress thread form, also known as the breech-lock thread form,[1] refers to two different thread profiles. One is a type of leadscrew and the other is a type of hydraulic sealing thread form. The leadscrew type is often used in machinery and the sealing type is often used in oil fields.
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In machinery, the buttress thread form is designed to handle extremely high axial thrust in one direction. The load-bearing thread face is perpendicular to the screw axis.[2] or at a slight slant (usually no greater than 7°)[3] The other face is slanted at 45°. The resulting thread form has the same low friction properties as a square thread form but at about twice the shear strength due to the long thread base. This thread form also is easy to machine on a thread milling machine, unlike the difficult to machine square thread form. It can also compensate for nut wear using a split nut, much like the Acme thread form.[4]
Buttress threads have often been used in the construction of artillery, particularly with the screw-type breechblock.[1] They are also often used in vises, because great force is only required in one direction.[4]
The image gallery below shows some of the types of buttress threads.
In oil field tubing, buttress thread is a pipe thread form designed to provide a tight hydraulic seal. The thread form is similar to that of Acme thread[8][9] the force is transmitted almost parallel to the axis and thread is about the same strength as standard v threads.