Oman: Airmail labels 2

Here are more airmail labels from Oman. A block of 4 and and couple of single labels.

Year: approx.1975, Gummed. Günter Mair's catalogue no: - OMN-A-2b, rouletted (wide steps), 
sheets, blue/white, 2**

Year: 1989, Gummed. Günter Mair's catalogue no: - OMN-A-3, rouletted (narrow steps), 
sheets of 50(5x10), light blue/white, 1*

Year: ?, Gummed. Günter Mair's catalogue no: - OMN-A-4?, rouletted (wide steps), sheets,
grey-blue/white,