How can the concave and convex cap cover the vacuum?
Do a thread fixture on the inside, and then through the external spiral inward force. Quit slowly. Just repeat it several times.
A spiral shaped continuous raised part having a specified cross section on the surface of a cylinder or cone. According to its parent thread shape is divided into cylindrical and conical screw threads; according to their position in the matrix is divided into outer and inner thread, according to the section shape (teeth) divided into triangular thread, rectangular screw, trapezoidal thread, serrated thread and other special shape screw.
