Australia Postage Due

Is someone can tell me what is the difference between a SG D117 type A and the other types that can exist ? All the D117 look the same to me.

I guess you don't have a copy of a Gibbons catalog?
Type A: Solid rectangle inside "D" (ptgs of 1/2d., 1d., 2d., 4d., and 6d. from 1909 to 1945)
Type B: Shaded area insde "D" (ptgs of 3d. from 1909 to 1945)
Type C: Solid segment of circle inside "D" (ptgs of all values below 1s. from 1946)
Type D: Six lines of shading above numeral and four below (ptgs of 1s. from 1909 to 1945)
Type E: Larger "1" with only three background lines above; hyphen more upright (ptgs of 1s. from 1946 to 1953)

Thank you very much for your answer and no I don't have the SG catalog. Nothing else in this catalog, specific to the D117 and different from the list of types you so kindly described in your answer ? Thanks again !

Or maybe all the SG D117s are of Type A and there is no utility to mention it. : )

The 6d exists with types A and C 'D'. That with type A is D117. That with type C is D125.
No single catalogue number has more than one type. Each 'type' has its own catalogue number.

Assuming that you have SG Watermark 15 (the C of A crown multiple watermark), then you only have the two options, D117 or D125. The Australian Commonwealth Specialist's Catalogue has a picture showing these differences, with D117 on the left, and D125 on the right:

The most obvious difference is in the shape of the inside of the D. However, you can also see a difference in the top of the curve of the 6. There are three dots/curves in the Original (D117), and only two dots/curves in the Redrawn Die (D125). So, first verify the watermark, then the shapes.

Very clear thank you to both of you !