3 3/8" X 4 1/2" (83mm X 110mm)

(dome incuse) SILVERTOWN    

  {Maker unknown}

Picture courtesy Bob Scafe

3 1/2" X 4 1/4" (86mm X 104mm)

No markings 

Picture courtesy Bob Berry

3 3/8" X 4 1/4" (83mm X 104mm)

(skirt incuse) Tri-delta / M / JS616 / 5N 

Picture courtesy Bob Scafe

3 1/2" X 4 1/2" (86mm X 110mm)

(dome)                

                             MADE IN ENGLAND

{Made by Bullers of England}

Picture courtesy Gene Kingsley

3 1/2" X 4 1/4" (86mm X 104mm)

No markings 

Picture courtesy Bob Berry