Abstract: A closure is used for selectively closing an opening of a container, the container including a tubular collar defining an opening and surrounded at the opening by an annular collar flange. An embossment includes a tubular collar retainer having an outer diameter slightly less than an inner diameter of the container collar and defining a through passage. A cap is threaded into the through passage to close the same. An annular retainer flange extends outwardly from an outer wall of the collar retainer and is seated on the collar flange incident to the retainer being inserted in the container collar. The retainer flange is secured to the collar flange by vibration welding so that the cap closes the container opening.