5 3/8" X 4 1/8" (135mm X 102mm)

 (skirt inkstamp)      

                                68

                                JAPAN

{NGK}

Picture courtesy Bob Berry

5 3/8" X 4 1/8" (135mm X 102mm)

 (skirt inkstamp)      

                                59

                                MADE IN JAPAN

{Unknown}

Picture courtesy Craig Polkinghorne

5 3/8" X 4 1/8" (140mm X 105mm)

 (skirt incuse)         

                              (around logo) MADE IN OCCUPIED JAPAN

{Shofu}

Picture courtesy Craig Polkinghorne

5 3/8" X 4 1/8" (139mm X 105mm)

 (skirt inkstamp)      

                             MADE IN JAPAN

                              54

{Shofu}

Picture courtesy Craig Polkinghorne

5 3/8" X 4 1/4" (142mm X 108mm)

 (skirt incuse)  

                       OTK

                       JAPAN

                       1967

{OTK}

Picture courtesy Craig Polkinghorne

5 3/8" X 4 1/4" (140mm X 108mm)

 (skirt inkstamp) 

                       (around logo) MADE IN JAPAN 64            

{OTK}

Picture courtesy Craig Polkinghorne

5 1/4" X 4 3/8" (140mm X 110mm)

(front skirt inkstamp)  

                                 MADE IN JAPAN

(rear skirt inkstamp)

Picture courtesy Craig Polkinghorne

5 1/4" X 4 1/4" (140mm X 107mm)

(front skirt inkstamp)  1958

                                 MADE IN JAPAN

Picture courtesy Craig Polkinghorne

5 3/8" X 4 1/8" (144mm X 104mm)

(front skirt inkstamp)  

(rear skirt inkstamp) 1960

                                 MADE IN JAPAN

Picture courtesy Craig Polkinghorne