SUZUKI Vintage Gas Tank Chrome Gas Cap model application unknown

SUZUKI  Chrome Gas Cap - Model application unknown.  NOS  New Old Stock.  SB79   Cap # 1

It measures approx. 2 1/2 inches O.D. on the top.  It is a push in rubber insert type cap and the rubber insert measures approx. 1 1/4 inch.  Hope these measurements will help determine what it fits. if any one knows what model it fits, please let me know.