2 1/2" X 3 1/2" (61mm X 86mm)

(top of ear) IFO 54 / H10

{IFÖ}

Picture courtesy Bob Scafe

2 1/2" X 3 1/2" (61mm X 86mm)

(top of ear) 819C IFO

{IFÖ}

Picture courtesy Bob Scafe

2 5/8" X 3 1/2" (64mm X 86mm)

(top of ear) IFO 55 / H1006

{IFÖ}

Picture courtesy Bob Berry

2 1/2" X 3 1/4" (61mm X 80mm)

(top ear incuse) IFO 40 / PBX 2J

{IFÖ}

Picture courtesy Bob Berry

2 1/2" X 3 1/2" (61mm X 86mm)

(top of ear) IFO 57 / D 100

{IFÖ}

Picture courtesy Bob Scafe

2 1/2" X 3 1/2" (61mm X 86mm)

(top of ear) N & 6L / SF

{Maker unknown}

Picture courtesy Bob Scafe

2 1/2" X 3 1/4" (61mm X 80mm)

(ear incuse)   

{Maker unknown}

Picture courtesy Bob Berry