Tonneau cover system

In a system for covering an opening in a structure, the opening having a periphery, the structure having sidewalls surrounding the opening and extending along the periphery of the opening, and the system including means defining a frame mountable on the sidewall so as to surround the opening, a flexible sheet for covering the opening, and connecting means for securing the sheet to the frame, the improvement wherein said connecting means comprise:

• a plurality of button members retained by said frame so as to be movable in the direction of the periphery of the opening and to be inseparable from said frame, each button member having a button protruding from said frame;
• a plurality of receptacle members each secured to the sheet and having a receptacle in the form of a pocket for securely but detachably retaining said button of a respective button member;
• each said button member comprising a base part held in said frame;
• said button of each said button member comprising an enlarged head part retainable in a respective receptacle, and a post supporting said head part on said base part;
• each said receptacle member having an opening disposed adjacent said pocket and dimensioned to receive said post of the respective button member;
• said frame having a channel for receiving said base parts of said button members in a manner such that said button members face outwardly from the opening;
• said enlarged head part of each said button having an exterior surface which faces away from said base part;
• and
• each said receptacle member comprising an elastically deformable retaining element arranged to engage said exterior surface of said enlarged head part of a respective button when said head part is in said receptacle of said receptacle member.