Bell 17.5x19.5 mm
Colour: black, violet
Items known:
8.2.1928 Askeröd to Montevideo MN (US), black
3.2.1934 Pkp 296 to London (UK), black
5.9.1949 SJP 7 Göteborg-New York to Worcester MA (US), violet
8.2.1928 Single rate letter to USA. Correct rate 25 öre. Shortpaid 10 öre. Amount due 2x10/1.00=20 centimes. Converted at 5 ctm = 1c to 4 US cents
The use of the due marking on thin item cannot be explained by the rates. It is probably philatelic.