These silver, 24-ligne retaining buttons are a facsimile of the Coast Guard Auxiliary seal. The threaded posts are screwed into the grommets on the silver chin strap and the frame of the Combination Cap, securing the strap without the need for a butterfly clasp or other retaining mechanism that might cause discomfort to the wearer’s head. (A "ligne" is 1/40th of an inch.)
Because Auxiliary uniforms are essentially identical to those worn by officers in the Coast Guard and Coast Guard Reserve, silver was chosen as the color for buttons and stripes rather than the gold used by those services, leading to the shorthand “Gold Side” and “Silver Side” to refer to Active Duty/Reserve and Auxiliary Coast Guard components respectively.